That's quite a large bedroom you have, U lucky bastard!
For a room that large it'll be a bit difficult for a small htib to fill it up with sound.
If you need an all in one solution (meaning receiver included) than take a look at the HT-S780 from onkyo. It is available at Circuitcity for 400$ (I think) or look on ebay. I owned the older version of this system (htr500, I think) and it worked quite well in my 17 x 14 bedroom. One caveat is, the sonic quality isn't that great. The receiver is top notch but the speakers are lacking IMHO.
Energy offers some nice little speaker packages named Act Cinema or Act6. I'm not sure on the price of those.
Now if it was me, I would head over to av123.com and pick up the x series package. You could get a 4.1 package and run a phantom center for under 600$. I know this is breaking your budget a little (and it doesn't include a receiver) but believe me it's worth it. I own a pair of xls and xsubs and these things kick some serious butt. Simply amazing what they did with a 200$ set of speakers and sub.
http://www.av123.com/products_category_pack.php?section=speakers&brand=55
Good luck and feel free to message me for further info.
JR