Captain America: The First Avenger is a solid post-conversion and a good title to get if you want to see a comic-book movie in 3D; it has a good sense of depth for most of its running time and a couple of nice pop-out effects.
Alice in Wonderland is another solid 2D>3D conversion that was shot with 3D in mind; a very imaginative movie chock full of interesting visuals.
As others have said, Journey to the Center of the Earth and Journey 2: Mysterious Island are two of the better live action titles available in terms of 3D. The stories are pretty goofy and the acting is, as expected, over the top but the visuals are top notch and both movies have plenty of pop-out effects.
Hubble 3D and Space Station 3D are two of the better live action Imax 3D titles and feature lots of great imagery from space; the 3D really suits these kinds of features well.
Giants of Patagonia is another Imax 3D title with some pretty intense dinosaur shots that will probably make you jump out of your seat once or twice.
The Universe: Seven Wonders of the Solar System is another fun 3D title that can be had for cheap and features lots of good CGI 3D imagery.
Xbox Live: XboxPhantom