I bought an Innova branded scan tool from Wal-Mart last year, does a good job reading and resetting codes, comes with website support if you need to look stuff up by make and model, etc...
I've played with the Cen-Tech ones that Harbor Freight sells, it really depends on what your needs are, if all you need to do is read and clear trouble codes their $60 works great for that, its about the same as my Innova, doesnt need a battery, just reads and clears trouble codes.
If you want one that can do a bit more of the diagnostics such as seeing real time data from the vehicle then your better off with the one they sell for $119.99, that one lets you see real time streaming data, handy if your trying to troubleshoot something thats intermittent because you can see the data change.
Or you can spend $50-$100 on the Innova brand ones that Wal-Mart carries, again on the lower end of the price range is basically a code reader that also lets you clear codes, on the higher end you can get one that shows real time data, lets you store stuff, and even connect it to your computer to print out data. The Cen-Tech lets you do that also, the one for $119.99 from Harbor Freight is the one a few shops around here have for basic troubleshooting and i have used it, works good.
