I put there a list of programs (with their use) for having a fast Desktop, and at the same time, this programs offer the maximum benefits as possible:

• Desktop Environment: XFCE4
• Web Navigator: Firefox
• Instantant Messaging: Pidgin (multiprotocol), Emesene (for MSN), Skype (VoIP, for talk with voice)
• Music: There are some alternatives. In my desktop XFCE I use quodlibet. You can try also Exaile (or amarok if you want to have some QT apps).
• Video: VLC or Kaffeine if you use KDE libraries.
• Burning software: Here is, or K3b, or K3b (xD) any other gtk app will be much worst.
• Imaging: GIMP (is there any other that can offer the same that it can? Krita doesn't like to me).
• Image Viewer: You can choose between Gthumb (GTK), GQview (very light) or Gwenview (KDE).
• PDF Viewer: You can use Evince or KPDF (for KDE). Please, never user Acroread, is a resource sucker!
• Office suite: Openoffice (I am not convinced by koffice, OOO is better).
• Text Editor: I use gVim because I am used to use it, but if you need something more user-friendly, kate or gedit are not bad.
• Develop Environment: I use Eclipse.

Well, I hope that list will be useful for anyone that cannot be decided about what programs he must install in his Linux.