Ive been using racechrono for a long time... It doesnt really matter (imo) what system you use, it will only be as good as the GPS receiver you get your data with. I recommend the qstarz 10Hz one mentioned earlier.
I have a crappy old windows mobile touchscreen phone i got off trademe for $10. Records the data, has bluetooth to connect with the GPS, displays laptimes, analyses data, that's it.
Once you've recorded your GPS data you can usually import it into any of the programs mentioned for data analysis. Performancebox, trackmaster, whatever. Racechrono even outputs data in a format directly readable for a few different programs to make it even easier.
A quality GPS is the only real cost factor, and it's only $100 anyway.
Here's a vid I made in a friends car. Racechrono video overlay data starts about 2 mins in.