I run AVG AntiVirus. I also use in this order: Spybot Search & Destroy, then AdAware. It sometimes takes both spyware programs to catch everything, although lately this has become less of a problem, with Spybot doing a better job of updates.
I don’t think I would ever trust a single program to find all the spyware, since some of those programs leave their own traces.
Exactly. Who better to plant spyware than the sole anti-spyware program on a person’s computer? Therefore, I run Spybot and AdAware like you, both to keep an eye on each other and in case one of them has some item in its database that the other one won’t catch.