Come one, guys! Cut the guy a break, even the best of us has had a typo at least once;
THe main question would be how much you willing to spend; you could start small by getting a Colt type bipod that attaches to the barrel, like a USGI M16 bipod, which is made of stamped metal.
SOmething like this is easy to find at Gunbroker or eBay and you don't need any adapters or a picatinny rail to attach it to the weapon.
However, the major concensus is that most AR15 owners have rails on their weapons and have a more stronger bipod, such as a Harris 1A2 bipod or a Versa-Pod bipod:
Versa-Pod with adapter.
Harris Engineering 1A2 Bipod.
I know most people I know have Harris bipods on their rifles and I am one that will get one installed on my AR.
But whetever you choose a harris or just a regular USGI metal bipod, is whatever suits you better.