I looked into Racepak and Autometers new LCD dash/logger. I determined that they were probably too awesome (expensive) for my needs. After a little experience with a DL1 I went with Race Technology Dash 2 Pro.
http://www.race-technology.com/dash2_pro_8_31379.html
The biggest reason I went this way is that I was already familiar with the software and having a DL1 in one car allows me to compare data between the two. They were also the only ones that said they could do point to point tracks, like an autocross. I got muddy answers from everyone else on that.
Driving your car and looking at a LCD dash and not using it as a data logger makes you a poseur.
I can't speak for others systems, but R/T has a OBDII cable that plugs right in and all the information is there. TPS, CTS, IAT, MAP, etc,
The Dash 2 will control video and overlay with the data. GPS is a must. I couldn't look at the data and remember what happened without the track map. Usually it is accurate enough to see the different lines you tried, especially awesome at autocross.
Every Sunday we autocross I load the data in the laptop to find out why my wife drives faster than I do
I then point out all the spots we both could have been faster and we pick a couple of things to fix. This week it was "use less brakes but brake more when you brake" and "quit coasting". Those are two things we never could have self analyzed without the data.
If I have time tonight, I get some screen grabs and post them up.