This photo basically says it all. Whenever I used my circular saw I covered myself, my workshop and my driveway in sawdust (much to the wife's annoyance). So I cane up with this to solve it on the cheap.
Step 1: Get the Gear
You will obviously need a circular saw, but will also need a small hand held vacuum (dust buster), and some suitably sized tubing. You can use a full size vacuum if you like, I used my little one because it's small and lives in my garage anyway. The tubing should be sized to fit the dust port on your saw (mine just fits inside the port, but you could get tubing to fit over it instead).
Step 2: Put It Together
Stick one end of your tubing in the dust port of the saw. Then squash the other end and jam it in the vacuum nozzle.
Switch on the vacuum and saw away! I was amazed how much dust it removes. I (and my drive) are lovely and clean now!