A dremel with diamond bits works without any problem.

Slowly is the trick. Doesn't matter what kind of glass.

Yep, diamond bit work great. Just remember to keep the spot wet. A spare hand and a squirt bottle works well. Keeping the glass cool helps prevent cracking. And go slow.

I buy weird vases and cachepots from thrift/discount stores and turn them into planters by drilling drainage holes in the bottom. They're usually porcelain, but drilling through glass is a similar process, with the same tools. I use diamond-tipped core drill bits and a hand-held electric drill.

This site gives really good, detailed advice on what kind of drill bits to use and how to go about drilling through glass/tile: www.diamond-drill-bit-and-tool.com/Diamond-Drill/MAIN.htm

--If you want a neat hole and have the time try using a brass tube as your cutter.. I learned this method from one of the Amateur Scientist columns in Scientific American, before they got all stuffy. Anyway a guy by the name of C.L. Stong was the editor of all the good stuff and he put out a book that describes this and a bunch of other neat hacks. I drilled a 3/8" hole in a 5-gallon water bottle using his technique and it worked great. Rough description follows.
1) Get down to an art supply shop or better yet find some amateur astronomers who are into grinding mirrors for telescopes and get some powdered abrasive.
2) Surround the area you want to drill with a dam made of clay.
3) Take brass tube and cut to a length of maybe 4 in. With a small triangular file nick the business end in a couple of places. Chuck the other end in a drillpress
4) With a small brush apply a slurry of abrasive and water to the surface of the glass.
5) Peck drill with the brass "bit" at a medium speed (for a 3/8" dia hole you'd want maybe 800 rpm), adding more slurry between each peck.