So, I'm about to order a TINI and start designing a board to host it and some interface circuitry.

What I have in mind is a smallish box (perhaps slightly larger than a tuner) that connects to the car player via ethernet, and provides the following:

Two serial ports, configurable as follows:
+/-12v RS232 on a DB9 (limited hw handshaking on one port, none on the other) via Maxim driver chips.
-or-
OBD-II interface via the appropriate ELM32x chip
GPS module
Dallas One-Wire interface
All sorts of sensors available for this interface.

Personally, I'm going to use the OBD-II and GPS options. The idea is to build a board that will allow you to stuff the components needed for your application, be it OBD-II, GPS, or whatever. I'd like to have one PCB that can be as generic as possible.

The TINI is, of course, field programmable, but I'd like to keep the code in the TINI as simple as possible, probably just a simple terminal server at first. That said, running GPSd and PPPd on the TINI have both been mentioned, and I'd like to see NTPd running there eventually.

I'm looking for input in two areas:
Which GPS modules should I support?
I have some Oncore GT's grabbed on the cheap from bgmicro, so I'll be supporting those for sure. What else do people have, or are available cheap right now? If I can get mechanical docs, I'll try to get a connector and mounting holes in the right place. If you're going to use an external GPS, you'd want to populate one of the "real" RS232 ports.

What am I forgetting?
The TINI has a CAN interface...anyone have a use for that?
Anything else that would be easy to hang off the TINI?

I'm not going to make any promises about how long this will take or what the units will cost (I'd have to sell kits...no way am I doing EMI testing) but I'm long overdue for a hardware project, and there are at least a couple of you out there looking for a way to do GPS and OBD-II simultaneously. And this is an excuse to learn Java.

Any and all input would be appreciated.