I strongly suggest taking a look at this tool: http://www.balsamiq.com/products/mockups
The Balsamiq tool is the best for doing mockups (i assume this is what you are referring too when talking about sitemaps before you start...). With this software you can quickly generate a working wireframe of what ever you are creating. So much functionality that you can actually share it with your client to get some good sign offs prior to typing the first bit of code.
Very powerful!
And the other one...just shown at the last MIX09 is SketchFlow. Couldn't remember it to save my life. This is a WAY COOL tool for site maps and UI mock up. I was trying to find you the actual MIX presentation as it is super cool to watch. But here are some YouTube videos of that presentation from a user perspective I guess.
http://www.youtube.com/watch?v=zsAZjb7FKXA
http://www.youtube.com/watch?v=f3ErrS68YMM
Check it out!
update...found the SketchFlow video!!! http://videos.visitmix.com/MIX09/C01F
Great keynote from there too: http://videos.visitmix.com/MIX09/KEY01