This plugin allows you to view a file in Sublime Text 2, and instantly open a browser window showing or blaming the file at the current line (on the current branch) on Github.
If you use Package Control, just install it from there. If not:
Clone this repo to your Sublime Text 2 Packages folder:
cd ~/"Library/Application Support/Sublime Text 2/Packages/" git clone https://github.com/buhrmi/githubify.git
The plugin should be picked up automatically. If not, restart Sublime Text.
Select some text (or not). Hit Shift+Command+P and choose 'View file on Github' or by keypress (⌘+\ by default, configurable in .sublime-keymap file). Shift+⌘+\ blames the current line.