i highly recommend OhmForces' Quadfrohmage. not just a simple filter. you can do some insane things with this one.
there's a nice filter called LittleDuck. it's one of those Synthedit creations, but it works fine. don't know the url, but google should help you
or check out www.audiodatabase.co.uk. i think you'll find it there, too.

cheers!

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