List of the most common folders in the iOS file system taken from http://forum.i-funbox.com/forum/main-category/main-forum/281-[ifunbox-s-feature]-no-jailbreak-ssh

ios-filesystem

Here's a list of the most common folders in the iOS file system. Please note, if your device is still jailed you are NOT able to see these folders.

/Applications
This is where pre-installed native apps and jailbreak apps are installed.

/Library/Ringtones
This is where the pre-installed ringtones are stored. User-purchased ringtones are placed in /private/var/mobile/Media/Ringtones

/Library/Wallpaper
This is where Wallpapers and Lockscreens are stored.

/private/var/cache
This folder contains cached data from applications, which can be deleted safely. A backup beforehand is recommended.

/private/var/mobile/Applications
This folder contains applications that were downloaded from the App Store.

/private/var/mobile/Media/DCIM
This folder contains all the pictures you have taken on the iPhone.

/private/var/mobile/Media/iTunes Control
iTunes stores its media files and preferences here.

/private/var/mobile/Media/iTunes Control/Music
This folder contains music and videos added via iTunes. Files are randomly renamed, but the content can be identified by reading the tags on the media files.

/private/var/mobile/Library/Summerboard/Themes
You can customize Summerboard Themes here.

/private/var/root/Library/AddressBook
This is where iPhone Address Book is stored.

/private/var/root/Library/Recordings
This folder contains audio files recorded by software like VNotes.

/private/var/root/Library/Ringtones
This folder contains ringtones transferred by software like iBrickr.

/private/var/root/Library/SMS
This is where text messages are stored.

/private/var/root/Media/PDF
This is where PDF files are stored.

/private/var/tmp
This folder contains temporary data.

/System/Library/Audio/UISounds
This folder contains audio files used by the user interface for various events.

/System/Library/Fonts/Cache
This folder holds all of the system fonts.

/System/Library/Carrier Bundles
Every carrier setting is here. Every folder has a shortcut with a number (from 00101 to 74810).

/System/Library/CoreServices/SpringBoard.app
SpringBoard is the standard application that manages the iOS home screen, providing graphical services ranging from icon badges, the dock, multitasking and so on.