Here's mine, no surprises:

Istock...43%
Shutterstock...32%
StockXpert...9%
Fotolia...7%
Dreamstock...4%
BigStock...4%
LuckyOliver...1%

Most of my productive images are on all sites.

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istockPhoto
Shutterstock
Dreamstime
Stockxpert
SnapVillage
Fotolia
BigStockP
FeaturePics
YayMicro
TheNextMicroWannaBe