I've been looking for an affordable 3D engine for a while, and Unity 3D has become my favourite one (and now you can get the indie version for free on their website). I've been away of game-ish projects for a looong time (except for a interesting multitouch application I've worked on recently), and hope to fix that soon. And Unity 3D seems a good tool/platform for that.
Although it helps to have a Flash and Director development background, I've found the documentation not so welcoming to newcomers. Luckily, I've found a book on Unity 3D (perhaps the first on the subject?) that is really helping me to get familiar with the tool.
I am still studying and learning from the book - and not so close to finishing it. But, so far I have nothing but good things to say about it.
The book in question is called Unity Game Development Essentials, and it was written by Will Goldstone. You can read a sample chapter here.