After installing Ubuntu 8.10

Additional Repositories

We are going to add the Ubuntu Partner and Medibuntu repositories which contain a number of apps.

From a terminal window, edit /etc/apt/sources.list...

sudo gedit /etc/apt/sources.list

... and enable the intrepid partner repository:

[...]
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
deb http://archive.canonical.com/ubuntu intrepid partner
deb-src http://archive.canonical.com/ubuntu intrepid partner
[...]

Then save the file.

To enable the Medibuntu repository, please do the following:

Import the repository:

sudo wget http://www.medibuntu.org/sources.list.d/intrepid.list -O /etc/apt/sources.list.d/medibuntu.list

Import the gpg-key and update your package-list:

sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update

Install software

Yes this all goes on one big long line --

sudo apt-get install amarok flashplugin-nonfree audacity azureus 
banshee bluefish dvdrip filezilla msttcorefonts gnucash gstreamer* gtkpod-aac 
sun-java6-bin sun-java6-javadb sun-java6-jdk sun-java6-jre sun-java6-plugin 
k3b kino mplayer mozilla-mplayer quanta kompozer scribus xchat-gnome 
bittornado bittornado-gui sound-juicer helix-player mozilla-helix-player 
googleearth acroread mozilla-acroread non-free-codecs ubuntu-restricted-extras 
libdvdcss2 opera xine-ui xine-plugin xmms2 xmms2tray xmms2-plugin-airplay 
xmms2-plugin-alsa xmms2-plugin-ao xmms2-plugin-asf xmms2-plugin-asx 
xmms2-plugin-avcodec xmms2-plugin-cdda xmms2-plugin-cue 
xmms2-plugin-curl xmms2-plugin-daap xmms2-plugin-faad xmms2-plugin-flac 
xmms2-plugin-gme xmms2-plugin-gvfs xmms2-plugin-ices 
xmms2-plugin-icymetaint xmms2-plugin-id3v2 xmms2-plugin-jack 
xmms2-plugin-karaoke xmms2-plugin-lastfm xmms2-plugin-m3u 
xmms2-plugin-mad xmms2-plugin-mms xmms2-plugin-modplug 
xmms2-plugin-mp4 xmms2-plugin-musepack xmms2-plugin-normalize 
xmms2-plugin-ofa xmms2-plugin-oss xmms2-plugin-pls xmms2-plugin-pulse 
xmms2-plugin-rss xmms2-plugin-sid xmms2-plugin-smb xmms2-plugin-speex 
xmms2-plugin-vocoder xmms2-plugin-vorbis xmms2-plugin-wma 
xmms2-plugin-xml xmms2-plugin-xspf vlc vlc-data vlc-dbg vlc-nox 
vlc-plugin-arts vlc-plugin-esd vlc-plugin-ggi vlc-plugin-jack vlc-plugin-pulse 
vlc-plugin-sdl vlc-plugin-svgalib thunderbird skype

You could also include

amule

A more detailed explanation is on HowtoForge.