Best Small Efficient Speaker for Office or Sm Room

I'm thinking of putting together a simple system for an office. A nice receiver or intergrated amp with tuner and CD player with small speakers placed on office furniture or speaker stands. I'm looking for a speaker that sounds good with very low power (25-40wpc) and at low listening levels. Another important part of the puzzle is that I don't want to spend more than $250 per pair used. Looking for some good feedback here. I'm open to any suggestions.
Axiom M3ti, Axiom M22ti, 93- 95 db eff. read the Soundstage reviews and buy new from Axiom's factory outlet. I have the M22ti's and love them,and great at low levels too. Money back trial period.
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:

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

A pair of used Tannoy Mercury M1s costs about $160 used.

Europen speaker of the year 1998 - 1999:

HiFi Choice review:
I think Superzero's are too bass shy.Try the ones.I have recomnded B&W 302's too freinds and use them on my all in one office set up.They don't have the bass the 303's have but are much cleaner and bright which I like.Really interesting technology went into them with a back panel with molded pyramids to break up standing waves.Last the cheap Triangle bookshelves (Titus?) get very favorable nods and are very efficient.Letus know what you got!
I think they would also be fine for a small amp in an office, but just to let you know that the later mentioned B&W DM303 which replaced the DM302 is not as efficient (88dB).