+1 for Little Snapper. I was a big Skitch user until I got LS as part of a bundle purchase. After a few uses I was totally hooked and haven't used Skitch since.
I do have to say though that Skitch is a *very* slick application and for most people will totally handle anything you need (doing it in style). Where LS shines is really in the library function where you can store and catalog your images. For someone like me who creates a lot of presentations and articles that's where it really beats Skitch. For just quick one off snaps I'd stick with Skitch.
Can't go wrong with either, but for power users I think LittleSnapper is tough to beat.
Wayne