The two big contenders I've played with were Gimp (yes, that's the correct website) and Paint.NET. Paint.NET is a super-sized version of MSPaint, so if you're familiar with MSPaint it might be the way to go. It took more resources so I shied away from it, so I can't attest to what it can handle as far as files. Having worked with Photoshop a bit I found it much easier to work with Gimp and that's what I stuck with. You can do some pretty amazing stuff with it, but I mostly just edit photos and apply effects by trial and error.
Ex-500.com - The home of the Kawasaki EX500 / Ninja 500R
A forum community dedicated to Kawasaki Ninja EX 500 sportbike owners and enthusiasts. Come join the discussion about modifications, cafe racers, racing, classifieds, troubleshooting, accessories, maintenance, and more!