Official City of Heroes Page -- Usually, the official site for a game is your first stop for a game and very quickly supplanted by other sites. City of Heroes, however, is blessed with a large, elaborate, and fairly detailed official site, with plenty of lore information on the game's background and signature heroes as well as enough information to get you started in the game without trouble. It also features such carrots as the entire run of the game's signature comic book as free PDFs, making the whole effect... well... super.
Official Forums -- Again, a pretty robust resource. The community managers do a great job keeping the forums clean, respectable, and organized. There are also solid community efforts to organize threads for things like supergroup recruitment, always a sign of an invested community.
City Info Tracker -- For all the controversy that surrounded World of Warcraft's Armory at launch, the core of the feature was a good one. City Info Tracker is a similar idea, allowing you to track badges, currency, levels, and so forth across all of your characters, whether you want it for signatures or just for personal information.
The Cape Radio -- An aggregate of several different podcasts, it also hosts a number of feeds for players looking for regular updates and a steady string of community events coming up.
City of Heroes Official Community Relations Team -- Want to keep up to date on the latest news but don't want to constantly be hitting the main site? Add this to your twitter feeds to get a steady string of updates and information, ranging from the serious announcements to some of the more entertaining forum diversions available on a given day. Updated steadily, as you'd expect from a Twitter feed.
Community Twitters -- The full team isn't the only Twittering resource for fans of the game. Two of the community representatives (Back Alley Brawler and Niviene) have their own feeds, as well as the former lead designer, Positron. While the individual feeds are (obviously) a tad less news-oriented, they're still well worth following for any fan of the game.
Paragon Wiki -- It's telling about the community team that they not only include official links to this wiki, but even mention it in the loading screen tips. If there's a better endorsement available to a fan-run service, it's hard to think of one. The site hosts detailed information about all of the game's villain groups, powers, and mission chains, as well as guides to lore and character creation. A better source of hard data on the game is hard to find.
VidiotMaps -- In all fairness, the official maps in CoH are pretty good, and certainly better than those in several other games. But they could still stand to be a bit better, and sometimes you really need to have an extra source of map information to plan where you're going. VidiotMaps has dynamic maps of every zone, complete with a number of useful points of interest already picked out and highlighted to lead you straight to them.
CoH Planner -- There are a lot of powers and slots to consider when you're leveling your hero or villain, and sometimes it's not immediately obvious what you want to pick. Veteran rewards and respecs help, but there are only so many of those. Luckily, there's the CoH Planner, which features both Mids' Hero Designer and SuckerPunch's online planning tool. The former is a download, but offers a comprehensive overview of everything you could want, including break points where Enhancement Diversification will start limiting your benefits from slots. Meanwhile, the online planner lets you quickly check on whether or not you'll run out of slots, or what powers you need to slot first.
Without a doubt, there are more sites out there that are both worth visiting and useful for the playerbase, but I'm not omniscient. So it's up to you, dear reader, to correct the omissions! Send any links that you know that by all rights should be included here to Eliot at massively dot com, and they'll be added promptly.