Here's my partial list; I'm still discovering stuff I've forgotten to reinstall (and will probably continue to do so for the next week or two). Unless otherwise indicated, I install the version from Ubuntu's repository (via Synaptic or apt-get).
- audacious - This is currently my preferred music player app on Linux. There's a different music player (Rhythmbox) installed by default, but Rhythmbox is rather bare-bones, lacking features such as an equalizer.
- ubuntu-restricted-extras - This is a downloader/installer for a random collection of useful things that can't be distributed as part of the core Ubuntu system due to licensing issues. Installing this package will automatically download and install various media codecs, Microsoft web fonts, the Adobe Flash plugin, etc.
- ttf-liberation - A set of alternative system fonts from Redhat. I like the look of these better than the ones GNOME/Ubuntu uses by default. After installing this package, I go into System -> Preferences -> Appearance, and set them as my default system fonts.
- openssh-server - Secure Shell server. I need this so that I can connect from other systems on my network using ssh, rsync, etc.
- compizconfig-settings-manager - I've decided to give the compiz desktop another chance. I figure if I'm going to try using it, I might as well have the ability to tweak its fifty seven bazillion desktop effects settings.
- smbfs - Although the GVFS/Fuse file system has gotten a lot better, and provides reasonably seamless access to Windows/Samba folder shares from the Linux desktop, sometimes you just want to mount a remote file system the old fashioned way. To do this for Windows/Samba shares, you need the smbfs tools.
- thunderbird - I like thunderbird better than the default evolution e-mail client. YMMV...
- VirtualBox - Great virtualization package for Linux. I install the proprietary version from the virtualbox.org site instead of the Open Source version that is in the Ubuntu repository, since the proprietary version has some additional features (and is still free for personal use).
- audacity - Decent audio editing package.
- lame - MP3 encode/decode tools.
- flac - FLAC encode/decode tools.
- apache2 - Apache web server. Nice to have a local copy running, to test web pages before uploading them to a public server. Also needed for the dwww package.
- dwww - Indexes the Linux documentation on your system and serves it up as searchable, hyperlinked web pages. After installing it and giving it some time to build the indexes, just open localhost/dwww in your browser to search or browse the system documentation.