Removing melted wax from glass is very easy. For a long time I had no idea how easy. You simply place the glass container with the wax in it into a dish of hot water (It does not have to be boiling hot, hot from the faucet is just fine) for a couple minutes and then the wax will just pop right out!
Additional tips from Sara and Stephanie Stepford:
If you remember ahead of time that your wax may runneth over then you can spray your votive holders with Pam before inserting the candle and any melted wax will pop right out.