Warren's suggestion is a good one. GIMP is fairly powerful and you can use 3rd party plugin filters like Eyecandy. As you can for the next 2 programs.
Adobe Photoshop (Elements) is powerful and feature rich as well but does cost more than a few dollars.
http://www.adobe.com/downloads/
Corel bought Paintshop Pro and that's a good program. I have used it for 10years now. U can down load a trial here and usually buy a copy for under $140 in a local shop like HNorman
http://www.corel.com/corel/