Well, a quick Google would find you a plethora of pages, giving you pretty much exactly the same thing - that is, AS2 to AS3 migration guides. A list of function name / class hierachy changes only goes so far, however - nothing seems to deal with the bigger problem - just how much AS3 has changed from the previous iterations.
If it was just as simple as changing function names it'd be easy, but there's a whole new set of methods for doing things, and often you don't know what you're even looking for to help you. Ever heard of
getDefinitionByName? Nope, me neither - but it turned out to be the function I was looking for yesterday.
Anyway, by far the best introduction to ActionScript 3 (not just the function name changes) is one I found from Senocular, Getting Started with ActionScript 3 (for Flash).