Avatar was cool in 3D, as was Transformers 3. Other than that, I haven't seen any really "cool" uses of it. Maybe the credits of Thor, but more so because I'm an Astronomy geek. The actual 3D in the Thor movie itself was laughable.
I think both Spidey & the Avengers were shot in 3D, so I'll give them a chance. I'd only see Titanic in 3D if I can be assured Cate Winslett's boobs are fully rendered.
"The Rich are there to take all of the money & pay none of the taxes, the middle class is there to do all the work and pay all the taxes, and the poor are there to scare the **** out of the middle class." -George Carlin