I have just discovered Xinorbis Disk Analyzer. I haven't tested it yet but I am interested in comparing it with TreeSize which is at the moment my preferred tool. I will mainly compare the speed of the scan for very big storage drives. Speed of scan is the key factor for me. Here's some default screenshots from this application which look very nice to me.
It can be downloaded from here: Xinorbis
I'll keep you informed with the results of my tests. If you already have an opinion on this product, just let me know!!