At this point in the US, there is no independent exit poll conducted for election verification purposes. The main national exit poll is commissioned by a media consortium (ABC, NBC, CBS, CNN, FOX, AP) and is used for commentary and analysis, not for verification of the official count.
The consortium releases only the overall results, which have been adjusted to match up with the official count. The consortium owns, and does not release, the base data from the exit poll (including precinct-level data).
The Vote Count Protection Project is trying offer an alternative, and is planning a pilot poll for November 7, with the goal of developing a national election verification exit poll for 2008. They are working with long-time pollster Kenneth F. Warren of St. Louis University and the Warren Poll. Steven F. Freeman of U Penn is a co-director of the Project. For the do-it-yourself version, see below.
In response to the large number of requests they've had, Freeman and Warren have written up basic instructions on how to do an election verification exit poll for anyone who wants to attempt their own poll - or who just wants to understand how an election verification exit poll should work.
The instructions are available as a pdf download on this page
One of the key elements in doing your own poll is starting with the correct information from your county election board, so if you are interested in trying this, or know someone else who is, they should get this information as soon as possible, starting tomorrow morning.