Don't overlook the Kef Reference Series. They are ported in the front and the newer versions have an adjustable boundary compensation selector that will further allow you to fine tune the base. I contacted KEF and they recommended that their speakers be placed no more than 12" to 24" from back the wall for best performance. My Reference 4s are about 14" and they sound quite nice, although I have to sit at least 15 feet from them in order to get the best base performance. Other "Class A & B" speakers worth looking at that are not overly sensitive to the back wall? -- many B&W speakers are also ported, as well as the Merlins.
See if you can find dealers carring your favorite ported speakers and then audition them by having the dealer move them into a position that will somewhat simulate your room. This may not be nearly as accurate or revealing as a home audition, but at least it will eliminate any real surprises. I once had a dealer do this with a pair of ML ReQuests and the speakers just died when too close to the wall -- so be careful with some speakers, and above all, go listen!
As several other posters have attested to, front ported or side firing woofer speaker are your best choice -- but what happens if you don't want a ported speaker? Then, you'll need to still pull the speakers out about 16" or so and instal base traps against the wall to kill some of the harmonics and base reinforcement from the rear wall. Also, if you must go close to the wall, then make sure you are not also close to the sidewall.
Finally, I fixed some of the problems in my non-treated, speakers too close to back wall room by adding a good sub. Even with full range speakers, a properly dailed in, a sub (REL, Veloydyne, Vandersteen, etc.) will help considerably.
Hope this helps, I went --Lorne
