I have been taking (according on peer advice) Fish Oil and Joint supplements on a daily basis since I started getting active and it's done wonders for my knees. I've been involved in quite a few painful mishaps in my life and as a result of that my knees used to feel and sound like those of a seventy year old man. Now they feel springy, there is no pain when doing squats and landing falls/jumps, and they sound a little less like kindling being slowly snapped in half.
Fish oil seems like a pretty generic sype of supplement, but for my joints I use
Move Free Joint Strengthener.
Check it out!