If you're doing disk analysis, you can use disk usage for windows. That presents its results in a traditional way, using a table.
If you're more interested in seeing your data from a higher vantage point, a higher level, then you need to perch atop great algorithms, and I've got a few pointers to two apps that do just that. These programs are fantastic, they give you a deeper insight into the common problem of a filled hard disk. Instead of clicking madly into each folder, you get a view that can be zoomed in and out: you're surfing the data space.
The first is called spacemonger and it shows you your data in varying sized multicolored boxes. It's an excellent implementation of an algorithm called a treemap.
Another fantastic program that also uses treemaps is called Sequoia View. This program has more options than spacemonger, you can put filters on the data and its prettier too ;) Sequoiaview can also sort on other things, not just disk usage, also on last modified time, last accessed time, etc. Spacemonger is simpler to use though, and that is directly related to the fact that it only has a few features, and they work well. Try them both out if you have time. If you're in a hurry just get spacemonger.
This treemap idea has successfully been applied to the stock market. You can see a java applet that lets you see the gainers and losers, and their relative change.
The second app is called Scanner. It's the same sort of idea, except that it shows you your data in a circle. Prett neat looking ;) The main attraction is easy to use, but I don't like the buttons on the right hand side, especially the one that empties your recycling bin. I'm afraid to go near it, as I don't empty my bin unless its getting full. Who knows when something in there might be useful later ;)
These are the future, and if you notice, they're all under 500kb. They're members of the tiny apps, and its because they've got the cool algorithms coupled with the slick implementations. Bravo!