Well, a 20-22" LCD will be higher than 1280 resolution, that's the first thing. Second, your budget of $300-$400 is very good and can get you a very nice monitor, definitely bigger than 19". Lastly, since you do gaming and movies, you'll need a monitor that will perform well on both. Often LCDs do good on one, but not the other. There are a few exceptions though.
Dollar for dollar, your best bet is a Samsung 226 (22"). Absolutely top shelf. I've used alot of different monitors, and Samsung is by far one of the best. Very fast response time so it's good for gaming, and no ghosting on DVDs. The backbleed isn't too bad, so black colors are quite black. Very sexy LCD, excellent color calibration software, very good color rendition, a nice big widescreen that runs 1680x1050 resolution.
Samsung 226 will fit into your budget no problem and is excellent. I highly recommend it. I have 2 225's and they are gorgeous. The 226 is even better.