Put two TBS of vanilla extract in an oven-safe cup/bowl, then place it in the oven at 300 degrees for one hour. Within twenty minutes the whole house smells like Heaven. It's actually a common realtor trick.
How to Clean Oven Glass - So Simple! Add about a 1/4 cup of baking soda in a dish and mix just enough water to make a slightly runny paste. Spread your mixture all over your glass (and the door if it needs it too). Wait 15-20 mins (or 30 if it's really bad) then wipe off. Any spots that may be left will wipe off with scrubbing pad. Voila!