The Super Ricohflex is about the smallest "Serious" TLR out there - indeed smaller than many 35mm SLRs with a lens mounted. The lens is a triplet but still very good. There are a few flickr "famous" photogs who have done really excellent work with these simple cameras. I would avoid the earlier Ricohflex models (VII, VIII, etc.) as they have a simpler/inaccurate shutter that often doesn't work properly, and the grease in the helicals is often rock hard on these older ones. Also look for a Super Ricohflex with the auto-stop option (automatic film counter) as this makes using the camera much more friendly.
I'm currently using a Reflekta II which is only a few millimeters taller than the Ricoh. I like this cameras very much, but expect the mirror to need replacement. Instead of an auto-stop, this camera has double exposure prevention - which is nice, but not as useful.
Smaller than either, the Lubitels. But I was not impressed by the lens on the one I had. Others however seem to have better luck. Variable quality I guess.