The best camera is the one you have on you and most likely it'll be your iPhone. Here is my list of resources for the best iPhone camera accessories.
5 Accessories to Make Your iPhone an Even Better Camera. Gear Patrol has assembled a great place to start assembling your iPhone camera kit.
If you want to step up your photography you need to invest in a tripod. Without a tripod mount it becomes near impossible to hold your iPhone steady. Manfrotto has created the ultimate solution. Check out the The Manfrotto TwistGrip here.