I just reupped my Netflix subscription after several years specifically so I could watch all the Avengers-related movies before seeing the new film this coming week, only to find that the only film available for streaming viewing on my computer is Iron Man 2 (which I enjoyed immensely). Iron Man (the first one) was rerun yet again on FX last night, as well, and I'd seen that in the theater, so it was sufficient enough a re-viewing as part of my Avengers prep.
So, I had to download The Incredible Hulk, Thor, and Captain America: The First Avenger. Of that, I've seen Thor so far. Much better than I had expected (although I'm still warped by Conan O'Brien's high-pitched Thor parody*).
The clips of the other two I've seen so far look pretty good too. I expect I'll enjoy all of them.