The biggest problems I have found on a video set with a digital still camera are poor auto white balance and noisy pics due to not enough available light. Shoot with the white balance set to tungsten, usually indicated by a light bulb icon, or daylight, usually indicated by a sun icon, depending on your primary set lighting temp. Buy a camera with a very low level of noise at the higher iso settings. The best I know of right now is the new Canon 5D. It looks incredible at high isos even at 3200, so you can usually get by without a tripod, plus you can shoot RAW with it. Also, the 20D will be widely available on the used market and it has better noise levels than the 10D. If you buy a used 20D, they are typically good for about 80,000 shots before needing reworked by Canon.
Having said that, on a much less expensive budget, I have the Canon S2IS. It does not shoot raw, but it does shoot superfine mode jpgs at 5 megapixels, which is more than enough for anything I’ve done. It has the flip out LCD and you can bump over to preview very quickly to zoom in tight to check focus. It has a 12x lens that I think is something like 32mm – 400mmish. It has Canon’s wonderful Optical Image Stabilizer built into the lens, which can really save you in low light or when zoomed in, unless you can shoot at 1600 or 3200 like the 5D. I always shoot in a fixed white balance and in manual exposure so that shot to shot won’t have slight inconsistancies.
Whatever you are considering, a great website for reviews of various cameras is https://www.dpreview.com.
Just a tip, I’ve heard a lot of bad about broken promises with Apple’s new program, Aperture. So, don’t rush out to get it just because you start shooting in RAW. Wait till some bugs are fixed and some good reviews are out there. After that, it looks very VERY sweet. I’ll be a user when it’s at version 2.
BTW, I’ve not used my camera in the way you are proposing either, this is just my 2 cents. I occasionally scout or document a set that I’ve designed for archive or self promotion. Primarilly I shoot product shots for web or that will be “Ken Burnsed” for video. Occasionally, I shoot a still of some static subject to use as cover in videos too.
Hope this helps,
Gary