Ibuprofen is another good all-around pain reliever/fever reducer/anti-inflammatory - if it works for a C-section, it'll work for a sore knee, I promise! Some people have stomach troubles from it, so if it's new to you, you might want to be sure to take it with food or milk - I've never had any problems with it, so I don't know exactly what they involve. Motrin is one over-the-counter brand name, or you can buy no-name brand too.
You also might want to consider taking a bandage to wrap your knee if you need to give it a little extra support.