Actaully some of the best pixel artists only use something as simple as Paint. It's crazy, but true. In fact it's better than using such high-powered applications such as Photoshop, Paintshop and GIMP (not so sure here, since I've only used it a select few times) simply because the tool tries to do too much for you often enough and some of the basic features are left out because the designers assume other uses.

"2 'Will's agree... MS Paint is better." <insert cheesy chime sound effect>