(apart from those with 1000s of obvious spammy links from Chinese government websites, which Google seems to have missed. Oh dear. What a successful algorithm that must be.)
If you know of spam sites I would strongly suggest you report them to Google via the link which Matt Cutts tweeted today [goo.gl...]
Matt Cutts also tweeted today: "we're definitely interested [in spam reports] and we'll be reading the feedback from the forms."