Once you've burnt your candle to the point where it won't light anymore, fill the glass with boiling hot water in a sink. The boiling hot water will make it easier to remove any excess wax, as well as the wick that's glued to the bottom. Find a disposable utensil or stick to help you push the wick off.
Please remember to use your sink strainer! You do not want hot wax or glue to go down your drain.
The glue should come off pretty easily, and look like this.
Update January 22, 2013:
I've since found a much easier method of removing the wax and wicks. See method 2 here.