For some more complex pictures, like most of my countryballs, I use the free online program Pixlr Editor, which is basically the cheap man's photoshop.
Sometimes, however, the quality of Pixlr isn't that good. Sometimes, instead of making png images, I like vectors (they're smoother). For that, I use the open-source program of Inkscape. Here are some examples of things I've made in Inkscape. SLD StampsDSAC Poster I also have some other things I use on occasion.