Easily one of the coolest automotive sites on the 'net is Trackpedia.com, and the motorsports community continues to flesh out this wiki with telemetry data. Back when we last checked in six months ago, the site had data for only one track, but Trackpedia administrator Billy Newport recently alerted us to the fact that there is now information available for 21 tracks - including venues such as Mid-Ohio, Laguna Seca, and Buttonwillow. Included for most of these tracks is a speed-vs-segment map (shown above), as well as speed and lateral/longitudinal acceleration graphs.
Most of the data is provided by use of a MSD/Racepak G2X data-acquisition system, which appears to quickly be establishing itself as the economical system of choice (and yes, we're aware that the term "telemetry" isn't quite accurate for such a system, but we're not going to waddle into a debate over semantics). Certainly, with the price of such technology continuing to drop, we can expect to see more of this information available as time goes on.