I would recommend checking out BaseCamp by 37 signals and also Client Spot. I've worked with both of those but prefer BaseCamp. One I'll be checking out soon will be My Virtual Business Office (
www.myvbo.com) so you might take a look at what that offers as well. The nice thing about Basecamp and ClientSpot (just like Google Sites) is that you can share access with your client and they can also use it to help manage tasks and projects you are working on for them.