Everyone knows about istock, shutterstock, fotolia and dreamstime. Some of the lesser known players are:

micro
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123 Royalty Free - Stock Image and Photo Subscription
Stock Photography Images at Can Stock Photo
Royalty Free Photos, Download Stock Photos and Images stock photo download royalty free

non-micro
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featurepix.com
ShutterPoint Stock Photography - Buy Photos, Sell Photos (actually it's micro or non-micro, your choice)
KeenImages - Royalty Free Stock Photos
Stock photography and royalty free images and photos from Alamy (hard to submit to)

I think these sites are good options to explore since they are not as saturated as the bigger ones. This gives your images a chance to stand out better.