Green Lantern and The West Coast Avengers
When The West Coast Avengers first appeared, I thought that it was a great idea.  There were too many members of The Avengers at that time to feature on a single team, so I loves the idea of a second group operating on the other side of the country.  I especially liked the idea of Hawkeye as team leader - he had always claimed that he could do a better job than Cap, so I was glad to see him finally get his chance.  Of course, these days, Marvel has completely overdone the concept, with new Avenger spin-off teams popping up on a regular basis.  It once was a big deal to be granted Avengers membership, now it's hard to think of many Marvel heroes who aren't a part of the team.