Blood for the Baron!

Founder Avengers: Hank Pym (Ant-Man, smaller Ant-Man), Iron Man (Tony Stark, original armor, space armor), Captain America (yay!), Thor, Wasp (red costume, pre-Heroes Reborn)

Nice DA, you sure do have a vast collection.

Thanks Paul
Other Avengers: Beast, Black Widow, Captain Marvel (posthumous member), Falcon (with Redwing), Hawkeye, Hercules, Man-Wolf (well, John Jameson is part of the mansion staff, right?), Moon Knight, Quicksilver, Sandman, Scarlet Witch, She-Hulk, Spiderman (Peter Parker, ugly costume, black costume), Spiderwoman II, Vision, War Machine, Wonder Man.

The Masters of Evil: Absorbing Man, Beetle, Ultron, Doctor Octopus, Scorpion, Whirlwind.

And an "expanded" membership, villains who haven't been on the Masters of Evil but I find they fit: Abomination, Blacklash, Blizzard, Kraven, Misteryo, Rhino, Venom and Vulture.

Great collection.

Thanks Steve
Now let's see the rest of the world around the Avengers, like the other two pillars of that world: The X-Men and the Fantastic Four.
X-Men: Archangel, Banshee, Bishop, Cable, Colossus, Cyclops, Forge, Gambit, Iceman, Jubilee, Longshot (not a mutant), Nightcrawler, Professor X, Psylocke, Rogue, Shatterstar (not a mutant), Storm, Strong Guy, Sunfire, Warpath, Wolverine.

Just like the Avengers have the Masters of Evil, the X-Men have the Brotherhood of Evil Mutants (here mixed with a Freedom Force member and an Acolyte): Avalanche, Blob, Crimson Commando (Freedom Force), Magneto, Mystique, Pyro, Random, Sabretooth, Sauron (not a mutant), Senyaka (Acolyte, and since Magneto was here...) and Toad.

Fantastic Four: Ben Grimm, Franklin Richards, H.E.R.B.I.E., Johnny Storm, Reed Richards and Sue Richards. I also have Ben in his "speedo" costume, but I felt the two Bens together in a picture so small didn't look good, and I like him more with the FF uniform. I still have the pic with him, if you want me to change it.

No Frightful Four, so let's go to the rest of the heroes.
Unaffiliated heroes (or those whose teams haven't enough members here): Beta Ray Bill, Black Bolt, Blade, Daredevil, Doc Samson (or is he just a superpowered civilian?), Ghost Rider (Dan Ketch and the Spirit of Vengeance), Hulk, Maverick, Nova (or is she bad for being Herald of Galactus?), Silver Surfer, Punisher, Spiderwoman I.