Here's my toolchain of choice for using git on the mac:

Tower (http://www.git-tower.com/) is simply awesome.

Diffmerge (http://www.sourcegear.com/diffmerge/) tames those horrible merge conflicts.

Kaleidoscope (http://www.kaleidoscopeapp.com/) makes viewing diffs nice.

Diffmerge and Kaleidoscope integrate nicely with Tower, for a nice workflow.