THUS.SPAKE.Z  Works just fine on my late '08 Macbook Pro core 2 duo. OmniDisksweeper does the job quite well and is now free. Go for it; it's a no brainer. I bought it several years ago and have used it many times without issues.  
(Version 1.7)

AKROBAT  Used to be a good app. But now virtually unusable as it constantly crashes on my Intel Macbook.

Ok on my PPC.  
(Version 1.6.1b2)

GORDON142  Well, WhatSize has a nicer interface, but DiskSweeper lets you use basically all its functions without registering, which means its still my tool of choice. Honestly, $7 is about the upper limit for an application of this type, I think, but everyone wants more…  
(Version 1.6.1b1)

SYHARRIS  OmniDiskSweeper works just fine, but I'd say WhatSize is really just as good....and it's free.

Don't know if WhatSize works with Leopard(yet).....I'm still using Tiger.

But give both a spin, and then decide if ODS is worth purchasing.  
(Version 1.6)

E_COMMERCE  I love the company, but they seriously need to offer more if they expect people to pay for this, given that their competition does the same thing for free. What does it do that WhatSize doesn't? I certainly don't see anything at first or second glance.  
(Version 1.5)

ANONYMOUS  Another vote for WhatSize, absolutely free. You can find it at www.id-design.com. Alternatively, Tiger users can create a simple Smart Folder with a few rules to immediately identify the big files ... :-)  
(Version 1.5 beta 1)

ANONYMOUS  awsome little, app, yes you can use the command line du utility, etc, but this little app is much more fun to use, finding those big files on your drive, is a pleasure!

try it out, this software company is great!@  
(Version 1.4)

CHRISBROWNUK  Personally I use WhatSize. I prefer the interface and the price (free!).  
(Version 1.4)

ANONYMOUS  Not worth the money. What this tool does, you can easily do with even just the Finder. Most of the time, you aren't going to be deleting large quantities of files that the Finder cannot see anyway. I could see this as marginally useful if your computer was a major mess and you had no organisation, but then you've got other problems than disk space. This would be handy if it was free. As it stands, it is not worth $15.  
(Version 1.4)

ANONYMOUS  Sure it makes sense. Can you tell the finders column view to sort by size? No you can't, it only sorts by name. Since the column view is the fastest way to dig down & find out where your hard drive space is being taken up, this app serves a purpose. I agree that theres no reason to spend $ on it, but it helped me clear HD space on a powerbook several times in the past.  
(Version 1.4)