Heh. Well, when I'm doing a D&D character, I make up a quick and dirty excel sheet to run my gear cost in, so I know how much I got left to spend. In M&M, I made a similar Excel sheet to the one I use in Shadowrun to keep track of all the points.
My sheet is quick and dirty, now that I've set it up, but it does the math for me. And since I do most of my gaming in a PBP format, I can just copy things over into a text file which I can throw up on the forum I'm on at the time. Honestly, it is nothing special. Just set up the calculations so it does the math for you on most things.