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 chips

ELM Electronics sells the ELM327 ($25 USD) that can communicate with any car's OBDII. [datasheet] [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.

ELM327-based software

knock-offs

"Imitation is the sincerest form of flattery."

sampling speed

The are quite a few tips for improving the sampling speed: