I will 3rd (4th?) what Turf said.... Rubbing alcohol with Q-tip for contacts, and Windex for the outside. I actually prefer Windex glass and surface wipes. Nice and easy, clean and smooth lol.
If there's permanent marker or stickers on the Cartridge itself, Goo gone will usually do the trick. Please, only use Mr. Clean Magic Eraser as a last resort. It will scrub the texture right off your cart. I've heard if you soak your magic eraser in water before you use it, it can lessen the abrasiveness. But honestly, just stick with Goo-gone and some old fashioned elbow grease.
-Retromangia