My Favorite Guides
This technique works. Use a heat gun. Don't try any of the dopey "hack" fixes, like wrapping your Xbox in a towel, running it without the fans, or putting it in the oven. This is iFixit - they show you the right way to do things. Their guides work for a reason - they know what they're doing.
You CAN buy thermal compound, cleaning solution, and even the screws & washers elsewhere, but these dudes deserve your cash.