The number one search request on this site right now is "XNA Engine," so here you go.
"Torque X" has been released. While the source release costs money, there is a binary-only version of the engine that includes documentation, tools and sample code.
I'm still evaluating it so I can't tell you how good (or bad) it is. I can say that it is one of the more complex managed-code engines under the hood, but with good reason. Making an engine is hard. Making a crossplatform engine is harder. Making a crossplatform engine where runtime allocations can kill your performance on one of the platforms definitely sucks.
If you've used Torque X at all and want to share your feedback, this is the place to do it.