Street fairs, expos, sporting events, parks... If you can find a crowd, you can find a great shot. People are usually doing something interesting, even when they aren't.
The main challenge with shooting crowds of strangers with a stereo camera rig is... well, the rig itself.
I've found it's almost impossible to use my rig in public without attracting attention, so instead of avoiding these inevitable conversations, I use it as an opportunity to educate curious onlookers about stereography. (I'll pass out my photo URLs and paper glasses, if I have some handy.)
View the complete set in the Photo Gallery.
An organizational note: Almost all of my Photo Sets will have a few people in them. This set is for stray "people shots" that don't belong to a specific location or event.