maternity clothes

I know this is abit premature as some of us are only just finding out we are pregnant...but I was wondering at what week do you normally switch to maternity clothes. I know most of us are just dealing with bloat at this point, but we are going to go through fall/winter and spring with our growing bellies and I'm hoping to not have to spend too much on a new wardrobe. When did you change to maternity clothes and any must have items you would recommend?