Marvel Multiverse is d666. I haven't read or played it - but from what I've read about it, it's a pretty conventional RPG design.
Marvel Heroic RP is less conventional - some people compare it to Fate, although I don't personally think they're as close as is sometimes mooted. I think it's a terrific system. Here's my adaption of it to MERP/LotR:
Middle Earth/LotR RPGing using Cortex+ Heroic
