http://www2.towerhobbies.com/cgi-bin...I=LXNN65**&P=0
6 Channels, FM. You'll have to buy a mixer to run single-stick controlled skid-steer or else you can get used to the weird non-mixed style. This leaves you with 4 channels of fun.
http://www.teamdelta.com/products/prod2.htm
This site has RC interface switches as well as motors, bearings, wheels, axles, etc. This will get you ON/OFF control. Not too cheap, but it's top quality. Did you know the guy operating that site has also been a judge at the SJ regional for a few years now? You may have seen him on TV as an announcer on Robotica (and no, he's not not Ahmet Zappa
For speed controllers, if you're 12V or under then RC ESCs are the cheapest. Otherwise you're in IFI Victor territory unless you want to rig up a whole bunch of relays for super-twitchy control.
Dan