Spinsheet, I also like the Weber thermometers. Simple, cheap, plenty accurate for most uses. If you don't have a Performer around to compare it to (not all of us have as many grills as Bman), maybe visit the Home Depot grill department with a tape measure to get a good idea of where it should go. Starting in 2013, all One-Touch Golds have the lid thermo.
You'll actually need two holes. Once you find the right size bit (I use a scrap of wood to make sure the thermo will fit through), put some masking tape on the target area, mark the spot, and drill the main hole. Then pass the thermometer and bezel through the hole, set it into the proper orientation, and push the registration tab into the tape to mark the location. Drill where the tape is dented and you're all set.