All automobiles manufactured starting in 1996 and sold in North America are required by law to support OBD-II. You can locate your OBD-II connector using this database
ELM Electronics sells the ELM327 ($25 USD) that can communicate with any car's OBDII.
[quicksheet] Yes, the datasheet confirms the obvious: it's based on the PIC 18F2x8x.
(ELM also sells several less-frequently used chips that each talk to only a subset of OBD-II vehicles: ELM320(PWM), ELM322(VPW), and ELM323(ISO). They each cost $14 USD)
ELM327-based hardware assemblies
ELM327 is the real brains, but it needs some interface electronics, an enclosure, and an OBDII connector to make it practical.
- freeware, polished user-oriented apps
- freeware, oriented to tinkerers
"Imitation is the sincerest form of flattery."
- OBDDiag.net makes an "ELM327 compatible" chip. It's a complete redesign, it uses a slightly different chip (e.g. on the USB version, the USB controller is built-in).
- Avoid chinese clones.    They're frequently sold on eBay.
The are quite a few tips for improving the sampling speed:
- ELM327 v1.0 and v1.1 were criticized for being slow. ELM327 v1.2 had some speed improvements, but ELM327 v1.3 probably had the most speed improvements so far.
- One issue in the past has been the baud rate, so it's important to make sure your software supports the highest baudrate that your ELM327 supports.
- Don't buy chinese clones, they're all slow.
- a number of other setting tweaks
- ELM recommendations