These may be kind of obscure, but I've actually had them on previous vehicles...
Geology themed:
Reunite Gondwanaland (google for it!)
Don't love geology? Upper Jurassic!
Tough Schist
Geologists make the bedrock
Back in my Trekkie days, I had "Klingon Warrior Academy" on the car.
Nowadays, it's cryptic vanity plates and a great big red Slipknot logo...
