Why are you looking for a really sharp lens for video? Are you shooting on a 1DC? Because that's the only Canon camera where a really sharp lens can make a difference.
Sorry cpc, but sharp lenses make a huge difference on a 60D. They also happen to increase the danger of aliasing and moire ruining your shot almost exponentially.
Cabrera, The only really good cost effective lens in your budget is the Tamron 17-50 f/2.8 without the VC. Another you can find used for a hundred more than your budget or so is the Tokina 11-16 f/2.8 AT-X Pro. After that, prices pretty much double to get much better sharpnes along with all the other finer qualities of great glass.
If all you care about is "sharp", the rebel kit lens (EF-S 18-55mm f/3.5-5.6 IS, under $100) is surprisingly sharp. Slow and crappily built, but sharp indeed, I'd actually say that just as sharp as any other option in that focal range. And it has IS too.
Now, if that's too slow, or if you hate cheap plastic as much as most people do, then... what c3hammer said