Watching videos or video editing? Probably the former. Haswell equipped ultrabooks should be out soon, but the previous generation will be cheaper, especially when the older models go on sale. Then it's just a question of what was the best ultrabook with a 1080p display released in 2012? I think you're going to struggle to find one new for less than 800 dollars. Sales might be your best bet, that or a refurb.
Anyway, as for what laptop you should consider I don't think any ultrabook really stands out from the rest, but ones to consider are the: Acer S7, Samsung Series 9, Lenovo X1 Carbon, Dell XPS 13 and Asus Zenbook. If you need one soon, you will have to consider lowering your desired screen resolution.
Someone just posted this on another thread: http://shop.lenovo.com/us/en/laptops/ideapad/yoga/yoga-13/
. Slightly outside your budget.Edited by Vigil - 7/3/13 at 4:49pm