Visualize files and directories
I use a program called Disk Inventory X. It has served me well for quite a while. And it's free :)
http://www.derlien.com/assets/main.jpg
If you don't mind working from the command line, the tree
command does what you want. It's more or less standard on Linux and comes with Windows. I gather it's not installed by default on the Mac, but it's easy to obtain.