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 crap out of the middle class." -George Carlin