You'll find a lot of cool KDE applications.
Sometimes I come across a cool slackware package at www.linuxpackages.net,
but I install the package from source anyway. (but their top10 is a nice place to look for apps too)
audacity (audio editor), kmess (msn), mplayer (media player), tsclient (terminal service client), tightvnc (vnc), qtparted (partition manager), mldonkey/kmldonkey (file sharing), kbiff (mail notification), smb4k (samba browser), and spamassassin.