I have a Giant handlebar mount that looks a lot like this piece from VO:
http://www.amazon.com/Velo-Orange-Ha...511203&sr=1-46

It's for a 1" bar, but works fine on my 3 speed's 7/8 bars with the pads included with it. It lets you mount any standard bottle cage, and it hasn't budged over hundreds of miles of dirt riding.

I also have one of these M-Wave mounts:
http://www.amazon.com/M-Wave-Plastic...7511181&sr=1-4
It slides around on handlebars, but it works great on frames. I currently have it mounted on the seat tube of my single speed.