TUAW:

The free iFixit app is a handy little app that gives your Do-It-Yourself repairs a big boost. This app comes from the teardown experts at iFixit, who delight in exploring the inner secrets of your favorite tech (or not-so-techie) hardware. The iFixit app helps you repair just about anything from toilets to garage door openers, cameras, cars, and of course, PCs and Macs.

As dumb as some of their whining about “repairability” is, their repair and upgrade guides are second to none.