Everything they need to log into your accounts. All of your accounts.
Your password, your email, your reminder hint

And I bet you are using the same password on most of your accounts, aren't you?

Please change your passwords... now.

You can use LastPass, or any other password manager program to help you generate new strong passwords. But, they are worthless if you don't do anything.

lastpass password manager


Edit April 2014: Oddly enough, I wrote this original post at the end of March, and now a week later the media is chomping at the bit about everyone needing to change their passwords: Ignore The Fear Mongering

The media is not even scratching the surface of why you need to change your passwords. They are just reacting to a server level flaw being handled by server admins.  There are much bigger reasons to update your login info, but it's taking me longer to write about it.