You knew this was coming, but I'm impressed with how it's done over on WoW-Achievements.com. With points to track and players to compare, it was inevitable that we'd have a site show up to track achievements, and here it is. While the Armory itself doesn't show individual achievements (yet), they've apparently come up with a way to figure out a number per player, and there's a worldwide player list (or at least a list of the 53, 901 characters they surveyed somehow). You can also post a pic of your achievement info, and they'll update it on the site. There's no way to see your individual stats yet, but if and when Blizzard adds that functionality to the Armory, we'll probably see a couple of sites show up like this, that allow you to do more with achievements and tracking them than the official UI does.
Of course, the Xbox 360 is the gold standard for achievements at this point -- while other MMOs and WoW have used the mechanic in their own way, Microsoft has built achievements into Xbox 360 profiles available online to anyone, so that's where most of the great web tools are right now. But the one that stands out for me, that I'd love to see replicated in World of Warcraft, is 360voice.com -- it basically creates a blog of what you've been up to on the Xbox that presents your activity in a readable, fun format. With Achievements build into the Armory, something like that could be easily used to power a timeline of your character, and let your friends see from day to day where you've been and what you've done. Lots of very cool ideas to develop here -- hopefully Blizzard will release Achievement info in an API sooner rather than later.