I've been contemplating the purchase of a wideband O2 sensor and data
logger for use in tuning the injection on my van conversion (
www.my.tbaytel.net/guskers ) and autocross car.

The two I'm gravitating towards are:

http://www.plxdevices.com/onlinestore_domestic.htm

and

http://www.innovatemotorsports.com/lm1.php

Anyone out there used these or similar devices?  They would seem the only
way for a hack like myself to accurately tune air fuel ratios.

I do have a O2 sensor monitor ( http://my.tbaytel.net/guskers/gauges.html )
and would agree with Frank C. that these are very inexpensive devices that
tell you a great deal about the health of your fuel management systems.
They don't however, offer much with respect to reliable assessment of A/F
ratio outside of 14.7:1

Here's a great article on the subject:
http://my.tbaytel.net/guskers/Real%20World%20Air.htm

www.autospeed.com by the way, is one of the best "techy" car mags I've come
across.  The subscription (online) was money well spent.  Their older
issues are free.