SpaceSniffer is a newer tool on the lines of SpaceMonger and WinDirState noted in older answers.
As of Nov/2012 SpaceSniffer is very mature (also see notes from last year in this other answer)

_{While my question was not really targeted at locating how the user may have used up system disk space,
I can see that this is a useful aspect of detecting wasted space too.}

From their webpage,

SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool.

1. Size of the elements indicates relative size of disk space utilized
2. Clicking on an element brings out more detail
3. Double-clicking on an element zooms into that area
4. Allows filtered searches (say by file extension)
5. Tagged view with 4 colours that you can designate and then filter the view by tag
6. Filter by file size or date...
7. Generate a report with the export module

IMO, SpaceSniffer is the good blend of WinDirState (which uses too many colour tones and SpaceMonger which is quite old now).

SpaceSniffer is a newer tool on the lines of SpaceMonger and WinDirState noted in older answers.
As of Nov/2012 SpaceSniffer is very mature (also see notes from last year in this other answer)

_{While my question was not really targeted at locating how the user may have used up system disk space,
I can see that this is a useful aspect of detecting wasted space too.}

From their webpage,

SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool.

1. Size of the elements indicates relative size of disk space utilized
2. Clicking on an element brings out more detail
3. Double-clicking on an element zooms into that area
4. Allows filtered searches (say by file extension)
5. Tagged view with 4 colours that you can designate and then filter the view by tag
6. Filter by file size or date...
7. Generate a report with the export module

IMO, SpaceSniffer is the good blend of WinDirState (which uses too many colour tones and SpaceMonger which is quite old now).

SpaceSniffer is a newer tool on the lines of SpaceMonger and WinDirState noted in older answers.

_{While my question was not really targeted at locating how the user may have used up system disk space,
I can see that this is a useful aspect of detecting wasted space too.}

From their webpage,

SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool.

1. Size of the elements indicates relative size of disk space utilized
2. Clicking on an element brings out more detail
3. Double-clicking on an element zooms into that area
4. Allows filtered searches (say by file extension)
5. Tagged view with 4 colours that you can designate and then filter the view by tag
6. Filter by file size or date...
7. Generate a report with the export module

IMO, SpaceSniffer is the good blend of WinDirState (which uses too many colour tones and SpaceMonger which is quite old now).

SpaceSniffer is a newer tool on the lines of SpaceMonger and WinDirState noted in older answers.
As of Nov/2012 SpaceSniffer is very mature (also see notes from last year in this other answer)

_{While my question was not really targeted at locating how the user may have used up system disk space,
I can see that this is a useful aspect of detecting wasted space too.}

From their webpage,

SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool.

1. Size of the elements indicates relative size of disk space utilized
2. Clicking on an element brings out more detail
3. Double-clicking on an element zooms into that area
4. Allows filtered searches (say by file extension)
5. Tagged view with 4 colours that you can designate and then filter the view by tag
6. Filter by file size or date...
7. Generate a report with the export module

IMO, SpaceSniffer is the good blend of WinDirState (which uses too many colour tones and SpaceMonger which is quite old now).