Depending on your size you will want to check out a couple of brands. If you're smaller 5'2 and under look in to Julianna bikes. If you're 5'3 and taller try a small Specialized Stumpjumer 29er Comp, hard tail (I own this one). If you can afford it, the women's specific Fate is well worth it. Another brand is BMC, the Teamelite TE02 (carbon) or TE03 (aluminum) they come with a Fox fork which has a remote lock out. It's handy when you're changing terrain. Engage the switch and the fork will become rigid(flat surfaces) and disengage it will become squishy.

When I ride, I like the bike to be nimble. Since you won't have the forgiveness of a full suspension bike, you will have to be picky about your lines.

Good luck and enjoy the process!