Champions Online

From Wikipedia: Champions Online is a combined free-play and subscription-based, superhero-themed massively multiplayer online role-playing game by former City of Heroes/Villains developer Cryptic Studios based on the Champions license. The game's rules and setting are loosely based on the HERO System ruleset. The base game is free to play while subscribers get access to more elements of the game. Non-subscribers can though purchase many of the subscription-only gear via an online shop similar to other MMOs.