A coolant pressure tester is a BIG help in tracking down leaks. I got mine at Sears. They cost ~$75 but are worth it since you'll use it a fair amount. I think it was Benzmac who recently posted the right way to tighten hose clamps : pressurize the system and carefully tighten just the clamps where there is leakage, and just till the leak stops.

I found 3 completely unsuspected leaks in my cooling system (all hose clamps which APPEARED to be tight enough) when I used the tester.

Do not pressurize too high or you can blow out the waterpump seal.