i personally dont like burton just because they are a big brand, but they are all good boards. It all really depends whether you like freeride, the park, or the halfpipe. Dont just get burton just because they have a good rep, do some research, there are many other great companies like Ride (my personal favorite), Rome, Forum, K2, GNU, Lib Tech, Nitro, Roxy (which specifically designs boards for women).
Some of the best boards under $400 are Nitro T1 (better for freestyle), Roxy Ally Mtx (better for freeride), Flow Mriad (freestyle), Head Pearl (freestyle), GNU B-Nice MTX (freeride), Palmer Jade, Atomic Tika, Burton Troop, Capita Le Tigre, Forum Craft (all good overall boards). I got these out of the "Future Snowboarding" magazine from October 2007.
http://ridesnowboards.com/boardfinder/
This link can help find a good board for you based on your gender, height, weight, riding style, and foot size. It will gve you the best board they think is right for you and the size (the size you can apply to any board).
I recommend Ride, they are cheaper and just as a good company as Burton.