Interesting that Innovate Motor Sports has not been mentioned yet. I have used the Innovate LM-1 for the past 4 years with great results and no problems. I am now upgrading to the new LM-2 dual AFR system. It has built-in growth potential and will log 32 channels on a flash card. To get all 32 channels you add various modules but that flexibility lets you buy only what you need now. You can add more as you learn and grow. I have been only using AFR, RPM, MAP, and TPS, in the past, but am now adding temperatures, frequency, and pressures.
The other brands mentioned are all good products and high quality. A few years ago they were out of my price range. Yeah, I know cost is relative to value received. I'm not knocking those systems at all. It is just that Innovate gave me a lower cost entry point to get started. I have not been disappointed. In my limited experience the Innovate system is not lower in quality. Innovate also has good documentation, downloads, and a technical forum with very good contributors.
This gives a good look at the modular system and pricing.
http://www.innovatemotorsports.com/products/MTS_grid.phpPS: BTW, click on "forum" in the upper right hand corner if you want to see the technical subjects covered. All great stuff and a free education! Between the forum and dieselgeek what more could you ask for