If there is a Jamis dealer in your area check out the Durango Race (or last years model the Durango 3). Jamis bikes are generally quite well spec'ed for the price and I am tired of being the only one around here mentioning it!!!111
Specialized Stumpjumper (if you can find a good deal on a last-year's model)
Cannondale Flash 3 (if you can find it for a discounted price) or Trail 2.
Keep in mind that most (or all) of the bikes available in your price range are made in the same handful of factories in China and Taiwan, and there is actually very little difference in quality from one brand to another. THe most important aspect of selecting a bike is making sure it fits you properly and you will be comfortable riding it. This is much more important than getting slightly upgraded components or hydraulic brakes instead of cable actuated brakes.
While the bikes that SlimRider mentioned are indeed great bikes for the money, be very cautious buying a bike over the internet for several reasons: it is difficult to ascertain fit of a bike online; warranty service can be difficult to access from an online company should there be any problems with the bike; most bike shops offer free service during the bike's initial 'break in' period, and for an online purchase you have to do this yourself. Basically, if you are comfortable doing your own repairs then thonline purchases are a better idea than if you are not.
However, you are form Texas and I have heard that BikesDirect bikes are available through some storefronts, possibly in your area, so the above warning may not apply to you.
Best of luck!