I would recommend the EASE Diagnostics. The $600 one that David spoke of is the Professional system. The stripped down system for the DIY guy is about $300 and is great. There are about 3 basic types, GM, Ford and Foreign, although I don't remember all their buzzword terminology.
You have the most expensive part, that's your laptop. I have an old Pentium laptop, probably about 4 years old with good batteries, and it is much better than a handheld scanner. You can keep records of each car incluiding extensive diagnostic information. Also, you don't need a code book, the tables are all right there with other diagnostic information.