This is a quick and dirty port of the completions generated by RubyMotion.tmBundle. As such, I'm not sure if there are any missing methods or not, but feel free to contribute if you find some.
Put this package into your Sublime Text 2 packages folder:
Windows: %APPDATA%\Sublime Text 2\Packages OS X: ~/Library/Application Support/Sublime Text 2/Packages Linux: ~/.Sublime Text 2/Packages
Because iOS is currently under a NDA you will have to generate the completions manually. To do this you will first need to update RubyMotion using the following commands in your OS X Terminal:
motion update
Now you can run the following command to regenerate the completions:
ruby ~/Library/Application\ Support/Sublime\ Text\ 2/Packages/RubyMotion/Support/compile_completions.rb > ~/Library/Application\ Support/Sublime\ Text\ 2/Packages/RubyMotion/RubyMotion.sublime-completions
Inside your RubyMotion project just start typing the name of a method and the autocomplete window will pop up. Press enter/return to trigger the completion.