Daisy Disk is the perfect example of one of those tools that should be built right into OS X.
It's the latest in disk visualization utilities -- software that scans your hard drive and lets you know which files are being hard drive hogs (in my case, World of Warcraft - no big surprise there). But, it's the added features that turn this from basic to "wow, why didn't Apple develop something like this?"
Once you initiate the software, you'll see a list of mounted drives on your network that you can scan. I scanned my main drive. It took less than four minutes for it to go through the 120GB drive and display everything in a circular graphic that does remind you of a daisy wheel.
Each section of your drive is color-coded for its specific purpose. The closest parts to the center of the graphic are the root levels. Going further out will net you very specific details on file sizes. Clicking on one section move it to the forefront and let you see everything on that level. When you get down to the files themselves, tap the space bar to preview the file. Then, right click to expose those files in the Finder, then do what you wish with them. Then, click on the inner circle to go back out to the level above. For smaller files and folders, it's better to use the list on the side rather than try to pick things out of the wheel.
Doing this enabled me to find large files that I hadn't seen in years, including a folder of old backups from 2006 that got carried over from my iBook. Deleting those netted me 7GB of space. The only feature really not working properly is the preview portion. When I tried playing .M4V video sources, I was rewarded with a grey screen. Regular .AVIs were fine.
DaisyDisk costs $19.95USD and requires OS X 10.5 or higher. You can do a full-featured download for free, which gives you a great taste of what it has to offer. For those wanting the same sort of tools, but for free, give OmniDiskSweeper or GrandPerspective a try.