Apple's Quicktime Movie Trailer Gallery - movie trailers in a variety of sizes
Atomfilms - a large collection of short independent films
Ad Critic - all ads, all the time (in Quicktime format!); unfortunately, this site is now by subscription only
Buy Telco Speed Test - they try to sell you optimizers, but they'll also tell you how fast your connection is
Shileds Up! - One of the great things about broadband connections is that they are always on. However, this may leave your computer vulnerable to attacks over the internet. This website has a couple of utilities which checks out how susceptible your computer is.
Macintosh RoadRunner guide - this is to help Mac users troubleshoot their RoadRunner broadband connection. Personally, I have had zero problems with it over the past 4 years. Maybe I'm just lucky.