I’ve used it, so I’ll suggest it: Screen Calipers. If you have ever debated holding a ruler up to your screen in order to make sure your design is pixel perfect, this is the tool for you.
It’s $30 to buy, but the trial version works just fine for what I do. I’ve never had a need to rotate the thing…straight pixel measurements works for me!
IconIco has a few other products available, but I’ve never used any of them. Has anyone else?