Whenever people start getting into photography and they want to ask me for advice on what first lens to get (beyond whatever lens came with the camera that is) I ALWAYS recommend a 50mm prime, usually of the f/1.8 variety. It's got basically the greatest price to performance ratio of all camera gear. It's simple and not particularly versatile, but that means it's also ridulously cheap for its quality.
There's a reason it's got the nickname "nifty-fifty".
Photo-a-Day: Year 6, Day 167 - Total Days: 1,993