Remember for Mac

Remember is a keyboard-driven app for quickly setting up reminders.

Remember lets you stash distractions away for later. You bind it to a hotkey (option-space by default) and whenever something unexpected pops up -- say you suddenly realize you need to stock up on milk -- you hit the hotkey, then type buy milk +1h and hit return. An hour later, you'll get reminded that you need to go out and buy some milk.