Best Small Efficient Speaker for Office or Sm Room

As I write this, I am listening to Axiom M3Ti's and feel that they quite capably meet your requirements for $275 shipped (new, ~$150 used). There was a lot of hype about these speakers about 2yrs ago, and it was well-deserved as these are solid little monitors.
They are remarkably well made at this pricepoint (very well-done laminate) and sound fantastic. I am using them in an office system driven with an Audio Refinement Complete integrated (50WPC) which is actually overkill. They are rated at 93dB/m with an easy 8 ohm load.
When I bought them about 1.5 yrs ago, they actually bumped my main speakers for awhile because the highs were far smoother and less-fatiguing than my old B&W's. They have impressive resolution, probably owing to the fact that they do not use a crossover - the 6.5" woofer naturally rolls off, yet blends surprisingly well with the titanium tweeter. You don't get much below 50Hz, but it seems like more with a punchy midbass.
This little system has an enjoyable presentation of most kinds of music - female vocals, jazz, chamber and acoustic music. It can even get you toe-tappin' with rock, but only in a small- to medium-sized room.
I have no affiliation with Axiom, and to be honest, I was seduced by the reviews. The only speaker that I demoed them against were B&W DM601s2's and it was an easy decision - MUCH better highs, a sweeter, more engaging midrange and much more refined. The B&W's were a little quicker, which was great for rock if only I could get past that hot tweeter. Needless to say, I am very pleased with my choice despite the relatively blind decision. Here's one of many reviews to give you a little more background on the design and the company's background:

http://www.enjoythemusic.com/magazine/equipment/0402/axiommillennia.htm

Good luck with your system - it can go a long way towards making those hours at work seem far less tedious. Mark

B&W DM302 are 91dB. No longer made, but mint used pairs very easy to get here and on eBay. Also a great sounding small speaker for very little $$$$ ($150 to $180 used). The cheapest speaker to have a Stereophile recommendation; an Editors Choice Award and Budget Speaker of the Year Award.

I use a pair of B&W DM302 in my office with a Creek 4330R (40 watts). See my systems link.

I have a secondary system consisting of a Linn Classik and a pair of B&W 303s. The 303s are a great little speaker, and you should be able to pick up a pair, even new, for under $300. These are "down the line" from the DM601s mentioned above, but check them out just the same. To each his own...

NHT. You can pick up some nice NHT's for very reasonable price (used). However, I would go for a fuller range NHT than the Superzeros. I own a pair of Superzeros and would not put them in my office. I also own B&W N802's and have run smaller B&Ws, Thiels, but for my office it's an NAD integrated and NHT speakers. Excellent at low volumes where they still seem to do the good stuff right.

second the Axiom M22Ti. I have been very happy with them driven by both a flea power zen amp and 300B tubes SET amp. Only missing is the bottom end.

Ake