On my work, I'm using Ubuntu Jaunty (9.04) server edition. As you might already using it, you will know that server edition not equipped (yet) with X server and desktop manager like KDE or GNOME. The reason I choose server edition are it's lite, and I can add only applications that I use. Desktop edition already fill with many applications I don't even use, and it's so heavy for my 256mb RAM!

OK, here are lists of applications I'm using, starting from X server and DM:
execute this first:

# sudo apt-get update
# sudo apt-get upgrade

1. X server and xinit

# sudo apt-get install xserver-xorg xinit xorg

2. WindowManager (either xfce4 or fluxbox, equal lite for me)

# sudo apt-get install xfce4

From this step, you can execute 'startx' to login to your Desktop Manager.

note: this step is optional, you can install any desktop manager you want: Gnome, KDE or anything.. as long as your computer is powerful enough :)

3. Mozilla Thunderbird - email client

# sudo apt-get install mozilla-thunderbird

4. Mozilla Firefox - internet browser
I make a writing about installing firefox here

5. OpenOffice - office suite

# sudo apt-get install openoffice.org

6. Network utility

# sudo apt-get install ssh nmap traceroute tcptraceroute dnsutils

7. CUPS (Common UNIX Printing System)

# sudo aptitude install cupsys

8. Samba - file sharing

# sudo aptitude install samba smbfs smbclient

9. Nautilus - file manager

# sudo apt-get install nautilus

10. File compression tools

# sudo apt-get install rar unrar zip unzip ark

With this 10 applications, I can do everyday office works. How about you? Please share your everyday usage applications on comments :)