I feel like the film industry has learned some valuable lessons in terms of using Digital 3D in film. I am, personally, an affable fan of the technique just so long as it is done correctly. It's like really good chocolate, but you can still overdo it. This Summer has found a certain measure of moderation, with X-Men: First Class, Super 8, and Cowboys & Aliens all opting out of Digital 3D. I think it's a worthy rule that if your film isn't just standard popcorn fare that you shouldn't go for 3D. In the meantime, there are some films that you could easily see in 2D without complaint. I'll try to give you a decent idea of which films would be worth the extra three bucks.
Thor - Post-conversion, but deals with epic celestial realms. Probably still majestic and preferable in 2D.
Priest - Not in 3D. Not in 2D. Not on DVD. NOT EVER!
Pirates of the Caribbean: On Stranger Tides - Promising visuals from Rob Marshall in service of a less than spectacular screenplay. If you see it at all, go for 3D.
Kung Fu Panda 2 - Heartfelt animation from Dreamworks, so definitely worth 3D.
Green Lantern - It's practically an animated film, and the superhero was made for 3D. Should attract the same fans as Avatar, so you'll see it in 3D either way.
Cars 2 - If it's not in the sky, it's not worth your time. If you see Pixar's latest, see it in 2D.
Transformers: Dark of the Moon - Sparks, explosions, clanging metal, and more explosions. Shut your brain off and see it in frantic 3D glory!
Harry Potter and the Deathly Hallows: Part 2 - I'm completing the journey in 2D. You should too.
Captain America: The First Avenger - Seems to evoke the film I would have died to see in 3D, Star Trek, so go for the glasses.
The Smurfs - Seriously? Don't even bother.