While i'm an avid Photoshop user... I'd have to agree that for most graphic work, both Gimp and Paint.Net (
http://www.getpaint.net/) are formidable graphics programs. Just because they're free doesn't mean they aren't powerful... ;)
I'd say you're pretty safe going with the free options. Most tutorials out there are for PS.. but Gimp has garnered a following so it wouldn't surprise me one bit to be able to find a slew of tutorials for it as well :)