My 2˘ - I use Avast!: anti-virus, anti-spyware, anti-rootkit and auto update for free. I loved AVG 7.5 but was lucky enough to read about all of the problems with v8 before installing it. I had used Avast! on my Vista side and installed it on the XP side. Zero problems.
I also use Spyware Terminator real time without the heuristics, and, no Web Guard.
SpyWareBlaster, not quite sure how to classify it but it protects real time without using any system resources.
Threatfire is supposed to be good but I haven't tried it.
On demand: SuperAntiSpyware, Spybot (no Teatimer), A squared free.
Lots of choices, limahl - best of luck!