Depends on your needs and resources but a few i use:
XFCE/FLuxbox - Window managers to handle drawing of windows etc.
Amarok - Excellent music player (requires KDE libs)
Gaim - Chat program covering most mediums (aim/ICQ MSN Yahoo)
Kopete (cause my gaim keeps losing ICQ ability) - Same as Gaim (requires KDE libs)
Azureus - Bitorrent client
Firestarter - Firewall
K3b - CD burner (requires KDE libs i think)
Gedit/joe/emacs - text editors
aterm - terminal
konqueror/gentoo - File manager
I also make a habbit of installing the NTFS kernel module to read my windows system (NTFS) partitionbut this has to be done everytime you install a new kernel
Some of the above come pre-installed (depending on your selection), some dont but they'll be something for every function