I've used adobe photoshop (way over kill for basic editing) jasc paintshop pro (nice but not cheap) and ulead photoimpact (not as expensive but less intiutive to use.
If you want to try something unique and completely free try downloading the Gimp. http://www.gimp.org
It's GPL open source software so its free to download and distribute as long as you include the original source. I've used it a few times, the different user interface takes some getting used to but its very powerful and free of course