norton dns, clearcloud, etc offer dns-level malware blocking as a primary feature.
opendns' features are speed, robust content filtering (and parental controls) and dns metrics (data about queries, queries per hour, etc) to their users. they also block widespread malware c&c servers (conficker being a good example)
one note about clearcloud - you might notice a degradation in performance w/clearcloud vs norton dns or other providers - comcast's peering w/GFI's servers sucks, and you'll often end up on an overseas DNS cluster instead of one stateside.
guessing that this topic should probably be in general topics though