Control-T(ControlT): Transpose (works in most Cocoa-native text fields and areas, but TextMate enhances the behavior).
Place your caret between two characters, hit ControlT, and the characters switch places (this is standard Mac behavior). Awesome for typos.
Select a word or series of characters on a single line, hit ControlT, and the characters in the selection will now be reversed (not too useful, but this is a TextMate enhancement)
Select a series of characters that spans more than one line, hit ControlT, and the lines will reverse. Characters within the line will still be in order. Most useful when selecting whole lines, but still works with partial lines selected, just so long as there is at least one newline character selected (TextMate enhancement).
