DON MORRIS  If you simply need to know what's taking up space on your disk, and you don't need a fancy chart to display it, OmniDiskSweeper is the app to use. It's free, Leopard and Intel compatible, and reasonably quick.  
(Version 1.7)

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)

ANONYMOUS  1. You don't need TinkerTool to 'hack' the system to show you 'hidden' files. All you have to do is go into the Finder's plist, and Panther lets you set this option on install.

2. But what have we with this disk sweeper? Basically we have a generic file browser watered down and severely limited to only want to sort by size, when any sorting by any other file attribute would often be as or more appropriate. Check out http://rixstep.com/4/0/xfile, http://rixstep.com/4/0/xscan, and http://cocoatech.com for ways this should be done. $15 is not gouging, but the app should be able to do more - after all, just to limit the functionality has cost them more code, not less. It makes no sense from a development POV, and it makes no sense from an end-user POV either.   
(Version 1.4)

KILIAN MUSTER  I got my copy with a bundle offer they had on a long time ago, where you could get the whole deal (OmniGraffle, OmniWeb, OmniOutliner, OmniDiskSweeper) for little money.

It is a very helpful app. Maybe I wouldn't have spend 15$ on it alone but as an additional goodie in the bundle offer it sure is a great utility.  
(Version 1.4)

MRRIVERS  Great app but too expensive for what it does.  
(Version 1.4)

JONATHAN  The Finder does not do the same thing as it doesn't show you invisible files like OmniDiskSweeper does (unless you are running in root, or have used TinkerTool to hack the system). $15 is way too much money for the app, I agree, but absolutely no one forces you to spend any money on it at all. This doesn't detract from the fact that it is very useful for determining which directories are eating up space on your hard drive...  
(Version 1.4b2)

WRAITHE  Tom wrote: "The Finder does the same basic thing, assuming you're running OS X."

Yes, and Disk First Aid does the same basic thing as DiskWarrior. Anyone out there believes this, save the money on DiskWarrior too.

This is a very nice Application it lets you see where all the space is being taken up on your machine's drives.

Very useful when you're trying to clean up and want to find out where your files are that are taking up a lot of space. $15? Maybe a bit much, and I wouldn't say "no" to a bit more cool Graphics (a'la DiskSurveyor, which is Mac OS 9 only), but it's been very useful in keeping my 400+GB of data organized and orderly.

"Finder does the same basic thing" What are you on?  
(Version 1.4b2)

TOM E M  The Finder does the same basic thing, assuming you're running OS X.

Open a list view window on your hard drive, enable calculation of folder sizes and sort by size with descending order. Expand the hierarchy as desired.

Now hit Cmd-Delete if you see anything big that really should be deleted.

Put your $15 back in your wallet...  
(Version 1.4b2)

KEVIN  The biggest mistake I ever made was paying $15 for a stupid ass progam like this, sure its nice that it can delete useless junk but who the hell would want 2 spend $15 on it. I thought it would have more to it, from my advice I would say deal with the useless files and wait till something free like this comes out later on.  
(Version 1.4b2)

ANONYMOUS  This program is *awesome* for cleaning up your hard drive. Works very well - make sure you register it so you can delete files directly from Disk Sweeper.  
(Version 1.3.1)

TREVOR STROHMAN  This app is seductively useful. Sure, it doesn't really do anything that you couldn't do with a bit of typing in Terminal... but who wants to do that when OmniDiskSweeper is so simple and inexpensive? I've never seen an app on any platform that makes cleaning out a hard disk easier.  
(Version 1.3.1)