At least adding sponsored to the keyword filter definitely works for those that have it in their filename (I haven't come across others yet.)

Edit: As a reference to others, also add iPod & buylegal to your keyword filters. eg: How to use the Keyword Filter

More to add: afford, finder & .com (be wary of using .com because some legitimate results may use it in their filename.)

And some more keywords to add to your keyword filter: More Spam Keywords for the Keyword filter.
And a couple of others: mp3-es.com & torrntazos.com