I bought a copy of Starcraft 2 from Amazon, and while I'm waiting for it to arrive, I'm curious: Is there a way for me to legitimately obtain a digital copy of it immediately?
Without your CD key you can't associate it with your battle.net account. Meaning no, there really isn't a way to legitimately play it without the key.
However, once you have associated the CD key with your account you can then download digital copies (if your sc2 cd's are scratched or can't find them).
Hope this helps and congratulations on buying an awesome game