As much as having obd2, steering angle, throttle etc in your data, I'd guess 99% of people will not even use it, so a regular cheaper lap timer and datalogger is more than enough. For example:
Aim Solo DL (no obd2) about $399 I believe:
AiM Sports - The World Leader in Data Acquisition
software is a bit hard to get used too at the beginning, lcd is monocrome only, predictable works well.
Qstarz LT-Q6000 will do the same as above retails same $399
LT-Q6000
The Qstarz can be had for way under msrp, vs the aim solo you are buying at MSRP.
Cons: no odb2 support
Pros: color lcd, green=faster, red=slower, predictable works well also easier to use software
Racekap G2x: tons of people run this one, very easy to see your lap times and segment if you are going faster or slower
cons: pricey but this can be found use for very good prices
Racepak Data Systems - Professional Motorsports Data Acquisition Systems
Racepak Iq3 datalooger/dash: works very well but damn expensive, this is what I run on my car along with a Qstarz lap timer.
has obd2 support ($$ for cable), and you can add any sensor you want to it ($$$), everything is programmable and has shift lights as well.
Racepak Data Systems - Professional Motorsports Data Acquisition Systems
Qstarz is one of my sponsors so if anyone wants a good deal I can hook you up with the Qstarz rep.
I found working with the racepak data is pretty damn complex so I don't do much analysis with it.