I do like my full size Iwata and understand that the touch up guns are just as good:

http://www.tcpglobal.com/spraygundepot/LPH50-G.html

I do disagree with Dave S (again, sorry Dave). A full size gun will allow you to change pattern size from about an inch to the full 8-10 inch spread and will allow you to do more projects while the touch up gun limits your usage.

The $10 Harbor Freight touch up guns,,,,,,,,,,

If you are only doing a few areas that aren't particularly visible, you can also purchase a Preval or two which is actually like a rattle can in that they give you a bottle for your paint which you screw it on to a precharged cannister and spray up to 16 ounces of fluid. These are about 5 bucks each.