some useful software I've come across:
DeVeDe - use it to create DVD's with titles, background music, images out of .avi's, mpegs etc..
QTerm - I use to to connect to places like CottonwoodBBS via telnet, works great.
VirtualBox- create virtual machines to test various other operating systems before actually installing on a real machine.
K3B- burn stuff to cd/dvd, if its not standard with your distro, you can always install it via *Ubuntu's software manager
Mondo- very damn useful. I use it to back up my servers to get a full image put on .iso's. Something goes wrong..boot disk 1 of iso's and restore the entire server from backup. Works with desktops, laptops, same concept.
KTorrent- if you download stuff via torrents, this is a great program also. Easy to use/setup.
E-UAE- Amiga emulator w/GUI interface
fs-uae- another Amiga emulator, in the under construction phase. Looks good so far.
OpenShot- video editor..you can put together family or whatever type videos with this, add music etc.
mypaint- if you like drawing..this is a nice piece to install. reminds me of Dpaint.
Audacity-audio editor.. I've used it to make ringtones for my phones