Check this out!!!!
Three websites for 25+ Photoshop alternatives
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11 Free Adobe Photoshop Alternatives (Softwares) | Tools
http://www.hongkiat.com/blog/11-free-alternatives-softwares-to-adobe-photoshop/
Photoshop Alternatives: Another 14 Free Image Manipulation Tools | Tools
http://www.hongkiat.com/blog/photoshop-alternatives-another-14-free-image-manipulation-tools/
One more site to check out for Mac based (non free) Image editors
Top 5 Alternatives to Photoshop For Mac Users | Psdtuts+
http://psd.tutsplus.com/articles/top-5-alternatives-to-photoshop-for-mac-users/