Lately, I've been dealing with my bad habit of using "that" in a lot of my sentences where it isn't necessary. Example:

He knew that she was going to be in a bad mood when she got home from work.
vs.
He knew she was going to be in a bad mood when she got home from work.

Apparently I'm not alone in this. I found a link to a great web page so I thought I'd share:
http://www.kriscramer.com/2009/the-unnecessary-that