Do not get a rear suspension - it may seem cool, but they are heavy, and if a bike at this price has one, it's garbage. A nice hardtail will suit you better anyway, rear suspensions are for serious action and make regular road and trail riding more difficult.
Brand is something you don't need to get hung up on. There are a lot of brands that make good bikes, including and not limited to all those mentioned so far. Your best bet is to head to your local independent bike shop and look around, ask them some questions and tell them your uses for the bike. If you can leave a license or credit card behind they will even let you try them out. An independent shop will not sell you a lousy bike, you will get decent advice, and you will get good support after you make the purchase. It's the only place to buy a bike.
For that price you can get a great hard-tail with 100mm forks and mechanical disk brakes. Again, if the bike comes with hydraulic brakes it will be at a sacrifice of other components at this price, and you don't need them for your riding, and they weigh more. If you want lighter weight in the bike that can still handle the trail, XC (cross country) bikes are probably your best bet.
If you still want opinions, write down some of the makes and models you found that you like, and then come online to see what people think about them before buying. Check out sources like www.pinkbike.com and www.mtbr.com.
