Up until now I have never really given checking for spyware as much attention as checking for viruses on my pc. Is this a mistake?
In my opinion spyware/adware/malware are much the same thing, and from what i've seen of friends and families PC's the non-destructive malware (adware) is more common than virus'. Personally I get hit by it very rarely, but that's mostly because I stick to browsing a few programming boards rather than general surfing.
Are there any good (reliable) spyware tools out there
Quick answer no, the word reliable does not apply to any anti-malware software. The first time you run adaware for instance it will claim to have found around 800 dangerous spyware installs, most of these will be cookies holding empty preference settings for adverts on banner sites. Yet it will still miss a substantial amount of genuinely malliscious software. No single tool is reliable, just like the anti-virus industry. Some are incompatable with each other, just like the anti-virus industry. And just like the anti-virus industry - the only sure fire protection is to know your task manager applications intimately and know how to remove the stuff by hand - as invariably that's what it will boil down too.
are they really neccessary if you buy genuine software from reputable dealers?
Not specifically rellevent but the point is in another context. It's more about what web sites your surf. P2P software is probably the most common source for malware infection.