I had the Extang Solid Fold that I liked quite a bit, before I bought my camper shell. Very durable, and leak free. My only complaint with it was that it does not fold flat against the back of the cab. If that's not a necessity then it's a great option, made in the U.S. too. I've been told the bakflip g2 is regarded as the best there is...but they're definitely pricey.
I think Extang just came out with a second generation of their tonneau, so it may have been improved.