depends on what you want to do with your board,
for carving, you want medium sidecut and something relatively long (more side cut means you can really lean in and rip some curves, less means you'll go faster but won't turn on a dime) also a good amount of camber is good here so you can really get an edge. if you set the board flat on the ground, a board with high camber will stick up in the middle about 1/4 inch. a dead board wont' stick up at all.
for the pipe or tricks, you'll want something that's totally bi-directional, not too much sidecut or camber and good cross-flexibility
for powder, you'll want something really wide, the rest doesn't really matter, except to make sure you can set your stance back just a little bit and you want a nose that sticks up high in the air
no matter what, a good solid base is important for speed and durability and i recommend buying a board that feels light so your legs don't get too tired
obviously i'm a carver, but i recommend something in the middle. mid side cut, average camber, pretty wide, medium nose and bi-directional. this way, you'll be happy no matter what the conditions. as for the company, they're all pretty good so whatever fits your budget and makes you look good!
here's a sample board you might like
http://www.burton.com/gear/pr_boards.asp?productID=164
here's a couple place to start shopping
http://dir.yahoo.com/Business_and_Ec...ng/Snowboards/