I beat San Andreas 7 times, 5 of them without cheats, and eventually reached 100% completion on one of them. I sold the game because I played it too much. It's too time consuming. They're so loooooong...
My favorite thing to do on there is enable infinite ammo, then stand on traffic on the highways with a rocket launcher. You have an automatic rocket launcher and plenty of targets. It's kinda like being driven in a rocket hog on Halo, but without the reload.