8 gauge is good to supply your amp with 60 amps. 4 gauge is good for 120 amps.
Check the size of the fuse your amp uses and reccomends, and make the choice based of this. For example, if it's a 25 amp fuse, 8 gauge will do you fine.
If you plan on expanding your system in a few months, such as adding another amp, run 4 gauge. You can split it later without much effort. Unless you are running a HUGE system, 4 gauge will generally do you fine.
i should be soon. i'm pushing 1250 rms as of right now out of one of my amps. my other amp is a 40x4 rms...right now i've got a 4 going to the cap, 8 off the cap to each amp. i'm gonna do 1/0 to the cap, and 4 to my sub amp, and 8 to my high's amp.