Originally conceived as a post solely concerning the extensive home brew work the website 'Atomic Think Tank' has done over the years, I soon realized the significance of this group's efforts would be largely dulled without having first given some background on the game they so persistently modify: Mutants and Masterminds.
Mutants and Masterminds (M&M) is a modern-era 'superhero simulator' based on the d20 System; a game style most commonly associated with D&D 3.0/3.5. By utilizing a free-form, point-buy character generation system, Players are given relatively free reign to create any sort of superhero (or villain, depending on the campaign) they desire. The information concerning this RPG is already out there in plentiful and detailed supply, so I'm not going to go any further into this background.
Edit: In spite of my previous statement, I'd like to take an additional moment and point out a common pitfall many first-time Hosts of this game encounter: Due to the openly creative nature of the character creation process, it's somewhat commonplace for experienced gamers to slip a 'broken' superhero past you. Though it's admittedly impossible to 'screen' every single concept presented for any unreasonably potent strengths, I've personally found the following hero themes to be most problematic:
1. Duplication/Excessive Minion Control: A character who can duplicate themselves or command a horde of allies to do their bidding will bog down and/or effectively control combat with their abundance of actions per turn.
2. Gravity: It was broken on 'Zatch Bell', and it's pretty cheap in M&M. Crafted well, there's little you can do to stop this hero without making a threat built to specifically counter their abilities.
3. Time: Oh lord, does this guy love to take the spotlight. Done in moderation (see: Dio Brando), this isn't too bad, but when you start seeing potential for rewinding/pausing entire encounters, it's time to suggest another character concept.
With the background of this fine game established, I'd like to draw focus on the initial focus of this post; the works of the group known as the 'Atomic Think Tank'. Now, these guys aren't just amateur aficionados, this prominent online community has been designated as the official board for all things M&M-related. However, what I feel makes them particularly interesting is their extensive work with in-game statistics. Between all their collective years of experience, this group has compiled an impressive database of famous characters (fictional or otherwise) configured for immediate M&M play. Feel like playing as Spider-Man, He-Man, or Optimus Prime in your next session? Wondering who would win in a fight between the Power Rangers and the Akatsuki? Chances are, the information needed for such a match-up is already available.