Mahalo comes to mind (there's some useful content, but there's also a massive amount of things scraped and barely cited or not cited at all). It may be unfair to call eHow a scraper site, but it usually ranks high for the terms and is very light on actual content, and again with the barely cited or not cited. Beyond that, I run into a lot of seemingly one-off sites that are geared toward a specific keyword combination, have no real content, but somehow manage to rank.

It's easy enough to ignore the big, repeat offender sites, but not so much for the one-off sites, and avoidable or not they're still there cluttering my SERPs.