The HKS Camp 2 is really cool. What I like best is how in addition to displaying info from all the stock sensors you can add more like boost, EGT and so on.
Here's something interesting I saw along the same lines from Garmin:
Garmin EcoRoutes ESP Displays Car Diagnostics On Your Nuvi GPS - ecoroutes esp - Gizmodo
It also displays info from all the stock sensors but instead of having to use a wiring harness they have an OBDII plug that is wireless Bluetooth. I don't think it's expandable like the CAMP but still cool.
To take it a step further I beleive Kenwood uses the Garmin software for thier nav equipped head units. It would be cool to see that feature integrated into the Kenwood stuff for next year. I think the CES show is Jan so I'm going to look out for that.