I'm in the same boat with cams being on my list of mods for the near future. I've done a lot of research on this subject, here's my thoughts.
Buying cams is like buying shoes, you need to decide what you want to do with them. Go to a formal party, run a marathon, play a field sport.
Once you decide what goals you have for your car then you can start to chose the cam specifications that will get you to your goal. Cam lift and duration are the 2 main criteria for choosing a cam. The more gross lift and the more degree of duration the more radical the cam is and the more posible HP to be made. From what I understand, the top suppliers of cams for modular mustangs are: Comp, Crower, Crane, VT, SHM, HP.