if you have a smart phone with bluetooth you can pick up an OBDII bluetooth dongle off ebay for like 5 bucks, then just download one of the free apps available like torque and you can read your codes and it will display stuff like rpm, coolant temp, vehicle speed, etc. it's actually pretty cool. I have it set up on my evo so I can use my phone as my wideband and boost guages.
it also lets you datalog to some extent.
here's a link to the one I have.
http://cgi.ebay.com/ELM327-OBD2-OBDII-V ... 230fe16dd7