Honda F-1: Honda's F-1 Web Site (as opposed to BAR's) is loaded with Flash videos (not downloadable) going back to 2001 when they were supplying both Jordan & BAR with engines. The debut of the BAR 006 for 2004 is shown as well. Some in-car included. You'll need to register (free) with the Honda F-1 web site, and have a fairly recent release of the Flash plugin to see them though. Look in the "Fan" section after you login.
Toyota F-1: As you might expect, since Honda's site has lotsa videos, so does Toyota's.
BMW Williams: Great section on the tracks to be used in 2004. The time lapse videos of the garage area is interesting. Quite a good selection of things to look at.
BMW Racing: The BMW World racing technology site has some great technical articles on F-1 engine and other technology. While you're at it, look at F-1 Technical Net as well. Nice to look at and interesting reads.
Jaguar: Jaguar doesn't seem to be showcasing its F-1 car, but it does have a pretty good video of a Jaguar SCV8 car. The photos of the Trans Am Jaguar look pretty good too. Click on "Latest Photos" link and scroll toward the end to see the Trans Am car. Actually, Jackie Stewart had a better site.
Renault: Renault F-1 has quite a few videos, but for some reason I can't seem to get them to work. Must be me. There are three different types to choose from but nothing happens for me with any of them.
Ferrari: Ferrari's entire site just doesn't work for me at all. Just as well. They're such a pain anyway. Their car should be so crappy.