Here's a filter I saw on Slashdot. Haven't tried it because the poster said it was overzealous.

[Adblock]
//(ad|commercial|marketing|promo(tion)?|shop|spon sor)s?//
/((double|fast|ad)click|click(xchange|sor))/
/(page|side|text)_?ads?/
/rcm.*.amazon/
/(adsdk|a1.yimg|akamai|amznxslt|atdmt|atwola|bilb o.counted|bizrate|bonnint|brides.ru|edge.ru|hit box|falkag|maxserving|promote.pair|realmedia|sant a.imho|servedby|spinbox|tribalfusion|qksrv|zedo)/
//ads?(.[w]*){2,3}//
/(ima?ge?|ad)serv/
/(ad|banner|sponsor)s?_?(id|ima?ge?|[0-9]*x[0-9]*) /
googlesyndication
us.yimg.com/a/
//buy_assets//
/[Wd_](top|bottom|left|right|)?banner(s|id=|d|_ )[Wd]/
/[Wd](double|fast)click[Wd]/
/[Wd]click(stream|thrutraffic|thru|xchange)[Wd ]/
/[Wd]value(stream|xchange|click)[Wd]/
/[Wd]dime(xchange|click)[Wd]/
/[Wd](onlineads?|ad(banner|click|-?flow|frame|im a?g(es?)?|_id|js|log|serv(er|e)?|stream|_string|s| trix|type|vertisements?|v|vert|xchange)?)[Wd]/
/(hot|spy)log/
/[W_](b(an|nr)s?|jump|redir(ect|s)?|stat)[W_]/
/W(cy|r)?c(ou)?nt(er|ed)?W/
/p(artner|ing.cgi|romotion)/
reklama
/sp(onsor|ymagic)/
/top(100|cto)/
/Dd{2,3}xd{2,3}D/