speaker recommendations for a 12 x 12 room?

Bdgregory, glad to hear it worked for you!

Pryso, I've found diagonal setups like you describe to often work well with planars, like Maggies and Quads. Now a dipole does have a bit smoother in-room bass than a monopole, according to an AES paper by James M. Kates, so the symmetry of a true diagonal setup is probably okay. But with a monopole speaker, my suggestion would be to not go all the way to a true diagonal but somewhere in between, to get the low frequency sources asymmetrical (with respect to the walls) in the horizontal plane.

That's my theory, anyway.

Duke

I recommend trying to stick with sealed boxed, medium sized book-shelf designs if you can, which blend easier in small rooms. Try to mate the speakers to the size of the space. Getting large speakers isn't a good fit, with too much boomy, bloaty bass energy YOU CAN'T get rid of! You can EQ it out a bit though. Nonetheless, I strongly recommend you get a Rives Audio "PARC" for your room,(you'll 100% DEFINITELY need one) to fix all your inevitable bass modes you won't be able to get away without having otherwise. In a "closed in" room, I also suggest some cooler running solid state gear.
If your'e trying to put your speakers right up against a wall, you'll be having some acoustical issues, that ported speakers designs don't really glean towards. A better blend with near wall speakers is acoustic suspension, sealed. If you are into some classical, instrumental, vocals, and some occasional rock pop, you can get into some panel or electro static speakers, if that's your cup. But, I say stay with medium sealed speakers, personally. If you go ported, consider putting em out in the room a tad more than perhaps you like (regardless of where the port is on the speaker)
What kind of music do you listen to however, and how loud(er, what's your life-style like?)? Do you plan any acoustic treatments? Cause if not, you should consider certain designs over others.
So, a few things to consider. But, with the 10 foot ceiling in that room, you can at least get 28-30" stands to work well, and have no problem at all with ceiling reflections- which often mandates more controlled dispersion designs, without acoustics on the ceiling. So your options of speaker design are wide open, otherwise -which is good.
So go listen to speakers you like, and maybe get em to let you bring em home!
BTW, what have you liked in the past?...

Personally, I don't like the idea of bigger woofers in that small room! It's like trying to fit a Mack truck into a small garage! Basically, there's gunna be problems.(mainly too much extra bass engergy to get rid of, without radical room treatments/construction - not practical.).
Trying to control the dispersion of your speakers by using larger woofers (that are likely focusing the sound in their respective regions more) I think is the wrong way of going about dealing with acoustical issues in your small space. There are certainly better ways to hear more "direct sound" than reflected than that. But, if you can't get the speakers out from the walls, and you have to have your listening chair towards the back, then consider something to break up the sound on the sidewalls then. (toe-in for tonality, not for reasons of side-wall reflections)
If you have to have your speakers up near the front wall, you can also move your chair out towards the speakers, which would help. However, you need to consider whatever position ends up getting flat response from your speakers - where ever that ends up in relation to your chair, and vice-versa.
I say find the speakers you want first, then worry about setup and acoustics

Iplaynaked, I realize that using large-diameter woofers in a small room is counter-intuitive. But then much of audio is counter-intuitive. For example, my suggestion to rotate the speakers-plus-listener triangle by about 20 degrees (resulting in asymmetry relative to the room's walls) is counter-intuitive, but Bdgregory found it to be beneficial.

Some of the acoustic challenges presented by a small room can be addressed through good radiation pattern control without over-emphasizing the bass region; in fact, those are two different issues. Some speakers systems with good radiation pattern control would have too much bass for a small room, and some would not.

In my opinion two issues need to be addressed in the bass region. One is the room-induced peak-and-dip pattern, and the other is room gain. I mentioned introducing some asymmetry to help smooth out the peak-and-dip pattern; to address room gain, you do not want a "flat" speaker; you want one with a gently downward-sloping frequency response. Typically, a sealed box will do a better job of giving you such a gently downward-sloping response curve than a vented box will. But... not always. "Typical" room gain is a 3 dB per octave rise below 100 Hz or so. If properly designed and tuned, a vented box can have a response that is essentially the inverse of that 3 dB per octave rise - and this can rival or surpass a sealed box as far as natural-sounding bass goes (a 3 dB per octave downward slope is impractical if not impossible for a sealed box). I personally favor bass systems that are somewhat user-adjustable, as the low frequency acoustic environment varies enormously not only from room to room, but from place to place within a room.

If designed to do so, a rear-ported box can give unusually extended, natural-sounding bass even when placed in or near a corner. Audio Note designs their rear-ported speakers for corner placement, and while I do think their specs are somewhat optimistic their speakers sound quite good in the bass region when set up as recommended. It's a matter of designing and tuning the speaker for its anticipated environment.

Duke

"But then much of audio is counter-intuitive"
Er, what specifically do you feel are "hard and fast rules" that are counter-intuitive, as you say? I believe everyone here would like to know, actually. I would

"Typical" room gain is a 3 dB per octave rise below 100 Hz or so.

Room gain is going to add bass boost to frequencies that are bellow the frequency,who's 1/2 wavelength is larger than the longest distance in a room (diagonal). This is going to be frequencies bellow 40hz in this room. Again, this is a better blend for smaller speakers with smaller woofers, not larger woofered (and most always lower extending speakers). Basically, larger frequencies aren't going to be properly represented in such small rooms.
I think most every acoustical engineer is going to concur, that in a small 12x12 room, smaller speakers (with most likely smaller woofers), that don't play super deep, will do better in a small space balancing in the room, basically. That's my input.
Also, since he is likely hinting at putting speaker nearer to walls than possibly ideal, I think 6db per boundary gain will make larger woofered and deeper responding speakers too boomy, indeed.
But he'll have to let us know how that works out for him...

"rotate the speakers-plus-listener triangle by about 20 degrees..."

Moving things towards a corner placement could indeed work out in a single seatting 2 channel setup, yes. But the speakers and response needs to measure pretty equal, and have an overall flat response curve to work. If that does, you're good! (as long as you deal with reflections, and normal aocustical treatment issues.(basically,all that's needed to build good sound in the setup.)
However,one of the main issues here would likely be that moving speakers and seats in this fashion, from an ideal standpoint, is that you'll most likely end up not being able to get similar response from speaker to speaker from the listening position. That's one of the main setup fundamentals that needs to be addressed. And that would be a main concern in any setup!
Simply stating that "moving speakers "20degrees", one way or another is NOT a hard and fast rule to properly setting up speakers!- I assure you. Yes, you could end up with good results, if your lucky.
But like with anything, it all ends up mattering what works and sounds good.
Still, you need to make sure that any setup offers flat response, from the overall system resonse. If not, you'll be up and down on the volume when things get too loud and boomy!...hearing too much boost at certain frequencies, and have an unbalanced sound. (I garantee no studio or well setup commercial cinema is far off of flat response for maximum accuracy and dynamic range - no matter what any audio witch doctor says)
In a 2 channel setup however, in an asymetrical room, there are benefits to getting your seat out of the middle of the boundaries, maybe off center. In this case, yes, your approach could end up working out. As long as the measured response is fairly even between both speakers, and they don't en up in "holes" or abnormally large bass peaks, and in relation to one another.
Overall whatever he can set up in his room, and attain BALANCED (yes, relatively flat response) sound, a properly distributed soundstage, overall sharp, detailed, dynamic sound with good sound-staging, then, he'll be good.
I still belive if he sticks with reasonable sized speakers, he's better off. But, if he goes larger, he'll have to adress the boomy bass, too slow sounding thick bass energy in the room, and, of course, bass modes and peaks and such.
Actually, integrating a sub with an EQ is always an option (that way you can tune the output of the sub, and EQ it to blend pretty descent.
Full range speakers don't give you this option so much.
Yeah, whatever works for yaz.....