There are many Armory sites out there, since Blizzard had the foresight to put the Armory data in XML so anyone who wanted to could use it in alternate presentations. 3D Armory is a new Armory site, just released into public beta. As you might have guessed, the focus of the site is on loading your character's data and displaying a 3D model of your toon; for instance, at top right you can see my death knight and how his gear looks in-game (yes, I'm still wearing my heirloom shoulders).
It does what it sets out to do, and does it pretty well: just select "eu" or "us" from the popup at the top of the page, type in your realm and character name, and hit go. Points off for having cryptic icons for all the functionality with only tooltips to indicate what they might do - I'm a big fan of obvious UI over flashy-looking UI.
Of course, like any site that relies on Armory data, it doesn't know what haircut or skin your character is using, so the model isn't going to be 100% accurate. Still, it's pretty good. As well as the central 3D model, it also includes a listing of all your items with gems and enchants - good for auditing people that are trying to join your pugs (for this reason, I wish there as a column in the item listing for item level).
There is some additional functionality revolving around voting on characters - on any character's page, you can vote the character "hot" or "not" (/sigh), and there's a listing in the right-hand column of the current hottest toons. This is a bit ill-conceived, but it doesn't really hurt, I guess. It's still a very handy and pretty fast site for achieving its main goal: displaying characters' gear in 3D. And it's still under heavy development, so more features will surely be added in the near future.