Folder Size for Windows adds a new column to the Windows Explorer details view that displays the sizes of files and folders. A service scans your hard disk in the background and caches the results. Designed for performance!
Seperate Window showing the folder size for Vista and later. Need XP for extra column. But still, pretty useful. Sadly I didn't find a way to customise the value the size is shown in. Apparently only in KB. Easy to read, thanks to commas, still a little annoying.
Can't believe Windows didn't have this from the beginning. Thank you and congratulations to the developer!