I've increasingly found myself using both GitHub and Bitbucket. In this vein, I just pushed up some changes to my list of Git utilities (https://github.com/mhartl/git-utils) that includes full pull request support for both GitHub and Bitbucket on OS X. In particular, if you're on branch foobar and want to issue a pull request to merge with master, you just type

    $ git pull-request

This pushes your local branch up to origin and opens the pull request page at GitHub or Bitbucket (depending on the relevant URL from .git/config).

The same Git utils repo includes git open, which opens the remote page for your project:

    $ git open

As with git pull-request, it works with both GitHub and Bitbucket (OS X only).