Reddit reviews Heads-Up No-Limit Hold 'em

ya husng.com is the best one, but i dont know if its necessarily worth it for the fundamentals you need at the stakes you are at. I'd recommend youtubing some videos, reading and posting hands on the heads up sng forum on twoplustwo and maybe reading colin moshman's book:

I've heard Collin Moshman's HUNLHE is good, I've never read it myself though.

Choose flatting his 3-bets if he's going crazy with them over 4-betting him back when in position. Position is the best tool you have in heads up, so use it. If he's c-betting 100% of his 3-bets, then try to flat with hands that make a good top pair hand, KQ, KJ, K-10 suited.. Just fold those Ace-rag offsuit hands. Flatting and playing post flop rather than 4-betting light is the lower variance play, and more useful when you think you have an edge on your opponent since you don't need to get into spots where you're gambling big when you're in position and have a solid read on his style.

Also, i STRONGLY recommend reading this book. It has done wonders for my heads up game, and overall understanding of poker. http://www.amazon.com/Heads-Up-No-Limit-Hold-Collin-Moshman/dp/1880685442