How can I convert a text selection to upper case in Apple Mail with a keyboard shortcut
Create ~/Library/KeyBindings/, save

{
  "~=" = uppercaseWord:;
}


as ~/Library/KeyBindings/DefaultKeyBinding.dict, and quit and reopen Mail. It makes ⌥= convert the selection or the word around the cursor to uppercase.

See http://www.hcs.harvard.edu/~jrus/site/cocoa-text.html or http://osxnotes.net/keybindings.html for more information.