Get the Whisker Dam here: http://www.whiskerdam.com/
I'm the proud owner of the Whisker Dam and I can say it's a Godsend for men with long mustaches. This small little copper shield fits perfectly on most beer mugs and coffee mugs. Keep it in the cardboard box and take it with you every time you go out for a drink.
The Whisker Dam is made out of a think copper cutout and has a cool patina affect going on with it. It's light weight and convenient. The only downsides I've run into with the product is the relative high price which is around $20 - $25, the fact it doesn't fit on all types of glasses/mugs, and every once in a while a mustache hair will be caught between the glass and the dam.
Beyond that, it's a really convenient product and will help keep the napkins at bay. I enjoy having mine around and recommend you pick one up if you are tired of your stache getting wet.