I've been using Git for a long time, and even though I love the power of Git's command-line tools there are some moments when a GUI is more convenient. In my case, I use SourceTree.app, by Atlassian.
Since I work on many different projects throughout the day, task-switching is a regular point of overhead for me. In this environment every second counts, so getting to the right screen of my GUI, even a few seconds faster, will make me more productive.
Using the following Terminal command, I can easily open whatever project folder that I am working on in SourceTree.app:
open -a SourceTree <path/to/repository>
Since I live in the terminal a majority of the day, this is a major time-saver.