I can recommend this
It's $50 and works with a laptop (or desktop if you're really desperate) and the OBDWiz software that comes with it is simple and fairly useful, the site has other software packages available and I bought the Ford enhanced one for $80 but it's probably not worth it, there are a lot of datastreams it should be able to look at that don't work for some reason.
Anyway, OBDWiz would allow you to look at real time o2 sensor operation as well as fuel trim information. Well worth $50 IMO, and although you'd need a laptop to use it, having the laptop screen makes it much more useful than the type of low-end scan tool sold at parts stores.
http://www.scantool.net/obdlink-sx.html