I've been looking into Unity recently and was seriously considering purchasing the Indie version, primarily because of its ability to run in a browser, but also because projects can be deployed easily to PC, Mac, Wii and even i-phone. And now with the release of version 2.6, it's been announced that the Indie version is now FREE to use. (The indie version was a cheaper stripped down version with a commercial license.)
Unity also features an excellent asset pipeline integration. While many engines make getting art assets into them a real pain, Unity works well. Assets are exported to project folders and unity converts them for you. Updating everything so you can focus on scripting, art and level design. It even has a well integrated physics engine and level/terrain editor. Even the documentation is pretty good.
With this announcement, its certainly the best low budget 3d game engine on the market and definitely worth a look.