The best bi-plane out there for 50CC is the Great Planes Utimate. It's available from Tower Hobbies here: http://www.towerhobbies.com/products.../gpma1307.html

Wow!!!! I just noticed Great Planes has a brand new Pitts Bi-Plane. That sure looks cool also.

For monoplanes you have a bunch in this class.
I'd start by looking at Wild Hare. They have Edges, Extras that are scale. The also have the amazing Sukhoi there: http://www.wildharerc.com/index.html

Aeroworks has a whole bunch of planes that work well in there also, including the Edge, the Extra, Bi-planes and Yaks. They also have a nice 50CC P-51. http://aero-works.net/store/

Troy Built Models have a great selection of RC Pilot planes and others. Mostly Edge, Yak, and Extras. Nice company to deal with. http://www.troybuiltmodels.com/

Another one is Extreme Flight. They have a new Extra and their great Yak. But you have to have a bit of a hard shell to fly these. But they do fly nice. http://www.extremeflightrc.com/

That ought to give you plenty of great planes to chose from. All of the above companies I've persoanlly dealt with and can give every one high marks in customer service and product knowledge. Any of them would suit your purpose well. The easiest to learn 3D with is the Edge. It's a sweetheart....but my favorite planes are Yaks. They do everything pretty good and are easy and fun to fly.

Hope this helps.
Thanks
Barry


PS: You may want to post this in the giant scale forum. You'll get a lot more replys there. http://www.rcuniverse.com/forum/forumid_110/tt.htm