Need an app that tells about file & folder sizes

I need an app that tells about file & folder sizes, like what is the biggest file and/or folder on my hard disk, sort this detail from biggest file and/or folder to the smallest & vice versa, also able to tell me about this detail based on the folder that I have chosen.

you can easily do this at the command line by executing the following at the root (/),

du -sk * | sort -nr

For directories only you can execute:

du -sk */ 

You could try Disk Inventory X.

Disk Inventory X is a disk usage utility for Mac OS X 10.3 (and later). It shows the sizes of files and folders in a special graphical way called "treemaps". If you've ever wondered where all your disk space has gone, Disk Inventory X will help you to answer this question.

I recommend DaisyDisk. Files and folders are visualized by a ring chart, makes it easy to identify which file/folder takes the most space in the hard disk.

The trial version has no limit on time, just a nagging screen when you launch the app.

You might be interested in GrandPerspective.