Needing software recommendation

I think you need to provide more detail--what do you do with your computer? What do you want to do? Games, graphing, or drawing fractals (http://freshmeat.net/articles/view/827/). Do you want to run Blender? Write text or math? Or program in BASIC?

Does xtartan still exist?

I would suggest either openoffice or staroffice - I think there's a wiki for good opensource software somewhere out there.

I use OpenOffice for just about everything. I'd recommend GearHead for games, but then again I pretty much have to say that.

I guess I should clarify ... I'm looking for stuff beyond the standard install (OO, Firefox, etc). Surprise me with something that's cool and has no (or exceeds the) Windows equivalent.

@ Pough

Xtartan! I laughed.

Subversion. Useful for way more than source code.

Not software at all, but you can install the fortunes-* packages, and waste some time with

$ fortune

or

$ fortune -a

for all (non-offensive and offensive) fortunes. It can also pick fortunes from certain topic.

gnome-panel has a widget named Wanda the Fish that runs fortune by default, if you don't like a terminal interface.

I also find gucharmap a fine time-killer, with its reference between characters ("see also"), and Unicode usage notes.

Filelight (I think it's part of out-of-the-box Ubuntu) is nice for inspecting disk usage. Konqueror has a view mode that show all files/subdirectories as rectangulars based on file size, the bonus is that it is a file-browser, you don't have to hunt for stuffs in two windows. It can split window into multiple views.

Pidgin (IM multi-client) is pluggable, many of the plugins are hosted on guifications.org.

Picard is a musicbrainz-backed music tagger.

Amarok is an awesome music player.

Don't run OpenSSH server on it until this is patched: http://www.sungate.co.uk/?p=314

OpenOffice is nice, but as most of my work is latex-based I use Kile (some colleagues prefer LyX). Agree with Hank: SVN is very good for collaborative development (not only for code - we use it for papers as well). Octave is a useful Matlab alternative. If you are into statistics, R might be the thing for you. I use GAP for computational group theory, but that might be just too specialized :D.

For audio I use rythmbox, for pics I use Picasa. For coolness, try celestia:
http://www.shatters.net/celestia/gallery.html

System -> Preferences -> Advanced Desktop Effects Settings

--

Be sure to give Tomboy Notes a few minutes' attention; it's much improved since you last visited.

gparted (actually, get the LiveCD version, its more useful when run without mounting any partitions)
amarok (ok its a KDE application but its the best music player out there IMHO), plus get the MP3 support etc. from Medibuntu)
mplayer - I've never got the default Totem media player to work very well.
firefox-2 (for some reason Ubuntu Hardy comes with a beta webbrowser by default!)

http://www.getmiro.com

Great for video podcasts and internet video in general.

Games: TeeWorlds, FunnyBoat, and Armagetron (Tron, yeah!)

Media apps: all the video players. VLC, mplayer, something that uses xine.

Burning CDs: K3B

I'm not sure what else I'd recommend, since I use KDE and don't know if you want to use K* apps... I play ksirtet (tetris) constantly, kmail, konqueror, amarok, konversation, koffice, etc...

Linux.com (former Newsforge) has some software reviews:
http://www.linux.com/feature/c4203

I've been using a combination of Lyx to write and JabRef to reference lately (as well as custom-bib to make reference styles). Definitely beats the Oo Writer/Bibus combo I was using before. R is evil, but that's most likely my lack of experience with it.

Otherwise there's Hugin to stitch together photos.

I'm a visualization geek, so these are the packages I like:
Gnuplot - A bit limited, but it can produce very customizable 2d and 3d data plots. If you learn all of the switches, your plots can be very well done. There is also a Python plug-in that allows you to use scripts to create plots. I used this tool to create ice thickness/velocity maps of Antarctica.
GMT(Generic Mapping Tools) - An excellent, but unfriendly, mapping utility. Harder to master then a GIS, but I think the results can be superior. This can also create very good 2d and 3d plots.
Grass GIS - A very good mapping tool. I use it to create maps from USFS data for personal use.
OpenDX - A quirky, but interesting, viz software that allows creation of content using plugable GUI components. The resulting visualization can be interactive. This is not as good as a custom programmed simulation, but I still think it is excellent and a lot of fun once you get the hang of it.
In the non-viz stuff:
XMMS - a mp3/ogg player that is similar to several mp3 players in windows. It is skinable and has a few visualization plug-ins.
AWK, SED, and Emacs - If I could marry software, I would marry all three. I guess that makes me a polygamist.
The GIMP and the Blender - Both can be a hoot.
All of those wonderful terminal utilities and scripting.

KStars astronomy program. Even if you're not into astronomy, you'll like it anyway. gFTP for data exchange is nice and one I use a lot. And need I say the word, "NetHack" or is that a given? ;)

I'm using KDE(which I would recommend), so these might not suit your GNOME desktop; but Kontact is a pretty good email/PIM suit. yakuake is really handy if you use a desktop environment but like to have a shell always at hand. If you are interested in network admin and/or evil, Wireshark and nmap are well worth your attention.

If you don't mind a little learning curve, LateX is seriously good stuff. It can be a bit baroque, especially once you dig into it; but typesetting systems are about a million times better than word processors.
Although they are a KDE thing, I'd seriously recommend looking into KIOslaves. Nothing too flashy; but enormously useful. DCOP/DBUS scripting is also a really cute feature.

http://www.getautomatix.com/ before it's deprecated. Installs some nice stuff like Picasa, Google Earth, Crossover and allows you to watch encrypted DVD's, the kind you rent.

Some random ones:

referencer
xaos (interactive fractal generator)
Liferea (feed reader)
gutenpy (gutenberg ebook downloader/reader)
Knowit or notecase for notetaking
qalculate calculator

Amarok for music.

Instead of automatix be sure to look at installing "ubuntu-restricted-extras" for all your mp3/dvd/codec/java needs.