how big a speaker can you put in an 11 x 11 room?

Large speakers are designed for large rooms, and small speakers are designed for small rooms, in general. Although you can use a large speaker in a small room, often you will have an overload situation with too much bass. If you aren't that critical of a listener, as the other posters say, you can use just about any speaker. If you are interested in the highest level of sound quality, look at the Unifield Model 3, just rated by The Absolute Sound as one of the best sounding speakers at the RMAF. The UniField Model 3 is an expensive speaker designed for small rooms. Read other posts on this speaker here: http://www.audiocircle.com/circles/index.php?topic=60302.0

Sorry to go off-topic, but in light of the last post, I am compelled to comment about the Absolute Sound. Buyer beware - since resurrected a few years ago, its reviews have become overwhelmingly positive, and positive in a uniformly over-the-top way. Take any two or three consecutive issues and read the reviews - pay no attention to that man behind the curtain.

I hope you don't mind that I answer your question indirectly, but I have some advice and recommendations that I feel are beneficial for your particular situation:

Consider using the Lyngdorf RP-1 digital sound processor.
This unit uses advanced eq to correct uneven response from speakers in less-than-ideal situations. Considering the equipment you use, I guess you might be apprehensive about inserting a digital processor into the middle of your audio chain, but I'm pretty sure you'd be far happier with the RP-1 than without it.
review: http://www.dagogo.com/Lyngdorf-RP1.html

You should read Cardas Audio's article on speaker placement in square rooms: http://www.cardas.com/content.php?area=insights&content_id=33&pagestring=Room+Setup+8

Consider room treatments, especially bass traps.

As far as reference quality, top of the line, small-room-friendly speakers go, you may want to audition the following: Magico Mini II, Merlin TSM-MMe/MXe, AAD 7001i, Usher BE718, and possibly the Silverline SR17.5.

If you crave the deep, powerful bass that bookshelf speakers can't provide (even in small rooms), a pair of subwoofers would sound more balanced than only one. I read that the Axiom EP400 subwoofer (8" sealed) is more articulate than the JL Audio Fathom F113 (13" sealed), although the former doesn't go as deep or hit nearly as hard as the latter. Regardless, I suspect that the 10" JL Audio Fathom F110 is just as articulate as the Axiom EP400. For ultimate speed and accuracy (and price) the Wilson Benesch Torus is another good option, although it hardly provides half the slam of the Fathoms and it takes up more space. Of course, the Lyngdorf RP-1 would allow you to seamlessly integrate any of these subwoofers into your system.

I hope I've helped.

Ohm Micro Walsh talls. I have a 11X11' room with 9'ceilings and it sounds amazing. It's all the speaker that you'll ever need for a room that size

No doubt I'd put a pair of OHM Micro Walsh Talls in there, build around that and be done. They are explicitly designed to go into small rooms in particular.

I use slightly larger OHM Walsh 2s with OHM Walsh 100 series 3 drivers in a 12X12 room. These work to the max in the room, but I suspect smaller and less expensive MWTs (or their shorter brothers, the Micro Walsh Shorts in some cases) would suffice.