Well, Naxxramas is big enough that I'll leave a whole article to it. The other raids from the original raiding scene of level 60 can fit into one since they're relatively easy to do. The roadblocks to finishing them are largely mechanical tricks, not damage output or survivability problems.
There's no real difference between the specs in these earliest raids. I run as destruction mostly because it's fast-paced, but any spec and almost any talent setup can do these raids.