CleanMyMac is a great tool for cleaning off your old cache, logs and other system files they you don't really need but don't want to mess with either. My first run I cleaned out 2GB of useless stuff.

Probably the best tool I have used for cleaning up my hard drive from old files and stuff I dont need anymore. I cleaned off 50GBs of old worthless stuff. Got more than 20% of my Macbook Pros HD back.