gitg - a GTK+/GNOME based git browser
gitg is an intuitive and fast local git repository browser targeting GTK+/GNOME. Very quick to view large repositories, and clearly shows branch information as well as diff's for each commit.
giggle - Imendio's GTK+/GNOME based git browser
Imendio's git viewer Giggle has a number of nice features like showing you commit trees and diffs. It is a great way to browse any local git repository.
Anjuta - Git plugin
Anjuta features a git plugin which supports git directly from the IDE.
Tk-based git browser
Upstream git's canonical repository browser is gitk. It's more limited in functionality than giggle, but is typically faster in what it does.
git-mergetool and meld
Git has this great feature which makes resolving merge conflicts easy:
Even better, if you have meld installed the mergetool will give you the option to load the diffs in meld. You will see three diffs side by side. The left diff is your local copy, the right one is the remote and the middle is the copy you edit. Once you are done you hit save and exit meld. You can now commit your conflict merge.
git-meld is a git command which can open a meld directory comparison between the working directory and any commit in a git repository, or between any two existing commits. This is quite useful for seeing what's changed over a series of commits.