It's free and open source, called
obdgpslogger. While you drive, it logs a lot of your engine parameters and your gps position, then lets you plot it out in google earth afterwards. There's also a CSV output right now, and I'm working on others [and more interesting number crunching]. There's a lot more info and background on the webpage,
http://icculus.org/obdgpsloggerBy way of example:

What you see there is a graph of where you were, how high the graph is is how fast you're going, and it's colored based on engine efficiency [eg, you can see the graph go red as I pull away from a stop, and green as I slow down to a traffic light].
I looked back, and I have posted one small component of it on these forums
before, here; most OBDII dongles are FTDI chips, and the default globalscale sheevaplug didn't come with a working FTDI device, so I wrote a userland tool that proxies FTDI chips to a posix pty. [which lets you basically use it like you would if there was a real working ftdi_sio kernel module]. For bonus points, this also works in ubuntu 9.10, which has a pathologically broken ftdi_sio kernel module.
I'll gladly answer any questions about this stuff, it's been my little spare time project for almost a year, now. To head off what I can only assume will be the first few questions;
1) In the traditional unix way, obdgpslogger comes as a
bunch of small command-line applications. You don't need a keyboard or display to actually log the trip, which is why it's so well suited to the sheevaplug.
2) Because of the design of the globalscale plug, it's easy to open up the device and replace the power supply with one more appropriate to your car.
The first guy to do this that I'm aware of logged the details on his site, here:
http://paulfurtado.com/hacking-sheeva-power.php.
Someone else did it and took photos here:
http://www.mp3car.com/vbulletin/worklogs/137079-connected-car-2.html#post1363722.
I will do it soon, now that I have a new ionics plug... But up to now, I've just been using the plug with a cheapie 110V cigarette lighter inverter.
You know what's funny is that I was going to post this on the "success stories" part of the forum when I saw the competition, and decided to enter instead :-)
Have fun,
Gary (-;
PS I'm generally avoiding talking about where the app is going in the future on the plug [there's some seriously cool stuff in the pipeline, hopefully], but the actual application that I won with is freely available as open source.