Not sure if this product was created to cash in on peoples' faith in the water-filled plastic bag, but I tried it a few years ago when we suffered a plague of flies and it seemed to work–they'd fill up with flies in days. But since it's a trap with a fly attractant, you put it where you don't want flies, not where you want to hang out. Oh, and does it ever stink!

http://www.rescue.com/products/fly.asp

Aaargh! This is something I thought of years ago. Although I must admit it is brilliantly executed.

Or you could use my one of my favorite-named products of all time, Tacky Finger brand fingertip moistener. I wasn't able to find a listing for the actual TF brand, but I did find places where it was used generically, as the category name for another brand of fingertip moistener. When I was the copy boy in a litigation law firm, I used me some Tacky Finger, let me tell you.

"The kit includes one of each of the following items..."

So they say.