Not sure how big you can go but in the SMALL category, I really like the nano sats, if you can find some more, go for it..
On the other hand, If you can stretch your budget a little and the size of these won't bother you, then do your self a favor and go take a listen to the PSB Imagine Mini series, you will be floored, I was, I couldn't stop listening to them. They are on my list and I will have a set soon enough, they are around 5x9x8 and when you get them in your hands they are tiny, not exactly bose cubes, but small...
PSB Imagine mini
heres a center on ebay cheap
PSB Imagine Mini C Center Speaker New Black MSRP $700 | eBay
I heard a 5.1 system with these and was really amazed, they had a pair of psb hd10 subs and if I didn't see the equipment before I heard it, I would have thought it was normal sized stuff, 2 tiny little subs, and 5 small speakers sounded really really good.. Then I had some time to listen to the minis in a 2.2 system that really surprised me as well as 3 other guys in the room...
As far as mounts go, I like the Omni mounts, they are kind of costly, but not prohibitively so...
Amazon.com: OmniMount 10.0WC Wall or Ceiling Speaker Mount, Black: Electronics they are sold eash so if you need 2 you need to buy 2, they have a bunch of different ones, but I had them holding a pair of cbm170s off the ceiling at a weird angle and they never skipped a beat...