I've mentioned this website before. Preditors and Editors is a good website for those of you sending out to publishers and agents. Though often slightly outdated, P+E covers pretty much every publishing agency, editor, or agent out there in terms of risk and legitimacy. It talks about some other stuff too once in a while, but that's the important part. This is the website to use so you don't get caught up in a scam. Because that would be stinky.
Where I've been using P+E for years, QueryTracker is a new thing I found. Basically, it helps you keep track of who you've sent out to, the deadline for their reply, and their responses. That way you can see just how pathetic you are! Just kidding, it's really, honestly useful. It also gives stats on various editors and agents, and some information about submitting to them. Good stuff!