James, the Fox line-up goes R, RL, then RLC. They stand for Rebound damping adjustment, Lockout, and (low speed)Compression damping adjustment. Mine is currently a TALAS (adjustable travel) RL, lockout is of little use on a decent fork, but the compression damping adjustment is very useful to have on a bike that does a bit of everything. If I had bought them new, i would have gone for the regular Float RLC. There is also RC2 which gives you seperate high and low speed compression adjustment!
The compression adjustment is very handy on more normal riding and trails as it allows you to run a lowish, more supple air pressure in the forks without them blowing through the travel when you pump the trail or brake.
Can't remember if I've mentioned it before, but Fox are supposed to be going over to 34mm stanchions for all the basic trail forks soon, as are currently seen on the 29er forks.