Wide band O2 sensor, the LM1 - ALELKS did it two years ago on the LTR, and it worked very, very well. With the right software package, he was catalogueing data runs to check his A/Fr during various runs, and different throttle positions. He went back after downloading the data, modified his tuning on the LTR (PIM and FIMAK), and had a much better running quad from the deal.
You can PM him on LTR Central or LTR HQ for the details. I checked his older posts recently to go back and review the data, and his old pics are down now, but the explanations are still up.
Good stuff. Bottom line? Make your own? Hell no, the products are already out there, and have been out there for a few years. Get the off-the-shelf stuff and save the headaches of developing a program that will catalogue the data. It's already done, man...