http://www.glass-holes.com/
I bought a great little kit there for $100. Has 5 or 6 hole saws that work great!! They range from 1/2" to whatever size required to drill a 2" bulkhead. Also comes with a fancy little stabilizer dealy with a suction cup to keep things still.
http://www.glass-holes.com/Set-of-Gl...aws-dhsall.htm
Great little kit... I love it. You could also just buy the one size that you need.