Mac OS X alternative to SnagIt

I've been spoiled by an application for Windows called SnagIt.  Its a really nice screen capture tool that lets you take screen grabs of portions of the screen, annotate them with arrows and boxes and text, then save or copy the result to the clipboard.  

I wanted something similar for OS X.  While I knew about "ctrl + command + shift + 4" to do screen captures of specific portions of the screen (replace "4" with "3" for the whole screen), what I didn't know is that starting with 10.5, Preview actually includes all the annotation features I need.  Thanks LifeHacker for this article (excerpt below)

Mac OS X Leopard only: One of the built-in Mac utilities that got the most feature additions in Leopard—albeit pretty quietly—is Preview, the PDF and image viewer. We've already covered how you can do more with Preview in Leopard, but Mac OS X Hints points out another good one: image annotation. Add arrows and notes, or circle and outline areas of an image in Preview using the Annotation menu. (In Preview's View menu choose Customize Toolbar, then drag the Annotate menu onto the toolbar.) Then, when you're editing a non-PDF image in Preview, just select your annotation, and click and drag on the image itself. Handy, and no third-party software required.

So, now to get the same features for when I need to sent an annotated screenshot, I just:

1. use the "CTRL+COMMAND+SHIFT+4" combination to bring up the screen grab crosshairs (use can press "space" after to get a camera icon to do a grab of a whole window)
2. Select the portion I want to grab
3. Open the Preview application
4. Either do "File / New" or "COMMAND+N", which opens a new document with the contents of the clipboard
5. Annotate away!