There is Battlefield Heroes that is meant to be released somewhere this year.
Last Friday I discovered Quake Live (I kinda feel ashamed not knowing about that one earlier)
Combine this with Unity3D and you can clearly see a change is going to happen in the world of web (browser) games.
Before there were only Flash games, some of which are excellent! But now you can have a full blown 3D engine running in your browser, how awesome is that!