You Perform is a set of add-ins for Outlook that look pretty useful.

Don't you hate when you send a message to someone about a file you are including, but then you forget to include the file? Then, you have to send a follow up email with the actual attachment saying that you are an idiot? One thing that I always wanted to do in Entourage (half jokingly because I didn't think anyone would go for it) was to look for messages where you refer to an attachment, but don't actually attach anything. Well, they've actually implemented this!

There's also one to help protect you against accidental reply-alls. That can be another bad problem. Jud, remember your accidental reply-all to that Belgium customer's email? :-)