Off the top of my head, with earth magic you can go in several directions.
Magnetism is earth magic, and taken to an extreme with Magic Senses you could start being able to perceive electromagnetic fields including radio signals, which would be an interesting slide toward technological Ferromancy (as mab called it). Eventually you could even develop this into electrical manipulation as well, in a sort of Earth & Sky union of opposites type thing. It's supposed to be a particularly impressive thing to master, like Harry being good at both Fire and Ice.
If you want to go more Mineral than Metal, straight up stone manipulation and mineral senses could have a wide range of applications, especially if the character has a strong Chemistry education. The Setting of your game will play a factor here, for example if you are in the Kentucky/Pennsylvanian region, in Alaska, or in the southwest near Texas or Oklahoma, there could be a lot of fossil fuels relatively close to the surface.
Offensively there are the direct sort of things where you create spikes of stone and make pits open up underneath people. Turing stone to sand or mud and back can be good too. Or you can take a more "seismic" flavor and go with shaking objects and using more Resonance effects to make things happen.
Earth Magic can be used to ground out other magic if you are extremely good at it, so there might be some low-level anti-magic protections you could use, though full immunity might be out of the reach of ordinary mortals.
Any strong Earth-sense could lend itself to riches through prospecting, even without active magic involved in creating or moving valuables to within reach.
Then there could be the spin of /being/ more earth-like, as opposed to more traditional wizardly stuff, bumping strength and defensive resistances, like what Sanctaphrax described.
A lot of it depends on what sort of role you'd like to have in your group. Are you the tank/bruiser? The Sensory information vector? The Jack-of-all-trades type bag of tricks that uses their surroundings against their enemies?