HoudahSpot - Search/Find utility for OS X that actually finds what I'm looking for, unlike Spotlight. Yeah, if I was a Spotlight pro there are probably commands to do all this. It's easier to spend money than time, though.
Plugin Authors: Toward a Better Future - I personally do not count breaking every plugin in the Rails ecosystem as "better." But if you've got a plugin that you want or need to make Rails 3 compatible, this is essential information.