I'll admit, I don't have a lot of experience with notebooks, therefore I don't have a lot of experience with notebook coolers. But experienced or not, I know that the Thermaltake Nbcool coolers are what I would look for in a notebook cooler. Light and effective, USB powered, quiet, and small enough to fit in a case or backpack, either the T2000 or T500 would do the job. Both use a very small amount of juice and won't overload your power supply or drain your battery.
Personally, I think that if I spent a lot of time using a notebook in coffee shops or the like, I'd probably choose the T500 for its smaller size. Other than that, I like the T2000 better. Either one does a good job, and would make an excellent gift for that friend or loved one or for yourself.
Both coolers can be found at online retailers, the T500 sells for between $18 and $25USD, and the T2000 is between $24 and $30USD.
The Thermaltake T2000 and T500 both earn the OCIA.net Seal of Approval.