Superhero fan here also and this has been a good thread. I liked Triggermv's original list and thought it was fairly close to my own, although I like the Thor movies better than he did. Regardless, I only have one disagreement with this thread and that is the statement below. I can almost guarantee (I'm sitting at 99.9% right now) that Marvel has NEVER considered Iron Man to be a "B or C" list character. He has always been on the A-team along with Thor, Hulk, Spiderman, and Cap. Getting Spidey engaged with this group is hopefully only going to do great things for this series. The Guardians are certainly a C or maybe even D group to Marvel that was a huge investment that payed off handsomely for them.
While I still believe in my “A/B/C list”, I’m not just magically making those statements up. What I’m referring to is also in nearly every special feature that Marvel has made about their movies because they, as well as everyone in the industry knew it themselves. It was pretty much common knowledge. Here are a couple great documentaries made by Marvel themselves to watch where they refer to it.
http://putlocker.is/watch-marvel-75-years-from-pulp-to-pop-online-free-putlocker.html
Check out around the 33:00 mark on this one to see them use terms such as “Marvel is rolling out the B-team”, Marvel is missing rights to a lot of their “heavy hitters”.
Here is another one where they talk about it too:
http://putlocker.is/watch-marvel-studios-assembling-a-universe-online-free-putlocker.html
Both are great documentaries by the way.
All said and done, everyone has slightly different definitions, but there are really very few “A” list comic book heroes. My “A” list really only includes Superman, Batman, Spiderman, Wolverine, X-Men (as a team, not individually), and maybe the Hulk (I truly think Hulk is B-list still), and Marvel didn't own rights to any of them (struck a deal with Paramount to do a Hulk stand-alone movie). "A-list" stars can essentially get thrown into any movie and regardless of whether the movie is crap, everyone will still go and see it. Outside of those, you are stretching. While it is hard to even think about Iron Man once being B-list, he was, which is why nobody can even think of Iron Man outside of Robert Downey Jr. and also why this whole venture was such a leap of faith in the first place that happened to just become a hit. Shoot, at least DC/Warner Bros owns movie rights to ALL their characters. These movies have just turned most these characters into A-list stars now. The A-list is much bigger now than it used to be, but superheroes in general are much bigger now than they used to be too.