I usually use MSPaint for pixel-work, like sprites that are small. If you want vector graphics, you can use paint shop pro (probably photoshop too), but it's not free.
All of the good vector art programs aren't free. >_<
A new version of it was released today too ...
gimp has most of the useful stuff from photoshop and paintshop pro.
but it is as Julius says free.
Go get it......go on!