9- Rhythmbox: Just as gtkpod is a great management tool for some aspects of the iPod, like iTunes, the music management side of things on a Gnome desktop is best suited for Rhythmbox.
For handling music management, creating playlists and having access to the album art to your music, Rhythmbox is very solid software. Bundle that with some fairly compelling plugins that do stuff like allowing for Pandora playback, it's easy to see why Rhythmbox is such a huge hit.
Plus, music stores are generally provided, Linux distribution depending. However, the single biggest let down with this software is not being able to sync your recently updated iOS device with it.
10- amaroK: Unlike Rhythmbox, amaroK is a lot more attractive to look at. Offering the same kind of functionality as Rhythmbox, I've found that amaroK goes a little further for KDE desktop users in that you can find scripts to try, in addition to the available plugins. To the end-user, this simply means even greater functionality.
So even though amaroK suffers from the same iOS headaches as other software thanks to Apple updates, it's still the best from the music management point of view. I'd even say it's better than iTunes from the perspective of overall music control.
11- Evince: Life without Adobe Acrobat Reader does exist! Even though the Adobe PDF reader has a Linux option available, there is a much faster and more user-friendly option called Evince. Faster, more stable and perhaps even more desirable than its Adobe counterpart, I've found Evince to be the best option for handling PDF files on my Linux box. The only real issue I've discovered while using Evince is an apparent problem working with editable PDF files.
12- Gnash: Like most people, I'm not a big fan of the Flash plugin for my browser. It's slow, CPU intensive, and even recent fixes leave much to be desired, as it's still a stability issue for many Linux users. The alternative is known as Gnash. It's designed to offer much of the same functionality as Adobe Flash player.
Yet I'd remind you that it's still a pretty young project and not necessarily going to meet with all of your expectations. I'd instead put most of my focus on HTML5 in the future. I think Gnash isn't really going to be the answer to Flash we had all hoped for.
13- K3b: Having used a number of disc burning programs available on the Linux desktop, I'd suggest that K3b is the best available at this point. Those who are familiar with Nero from their Windows desktop will feel at home using K3b. Much of the same file/music/ISO burning functionality is found here.
Based on my usage, the only thing I'd love to see added is a Blu-ray burning option. Not asking for the playback of DRM content, rather ripping data to Blu-ray discs instead. Considering Nero for Linux offers this option, I'd love to see K3b offer the same if possible.
14- Inkscape: Because not everyone is ready to use an Adobe product, users of the Linux desktop are left to think outside of the box. This means that instead of using Adobe Illustrator, for example, you’re more likely to find Inkscape providing much of the same functionality. Like with anything, there are going to be different approaches between the two software programs. But for someone not schooled heavily in Adobe, learning to use Inkscape is very simple.
As for possible disadvantages, the only thing I would point out is that Inkscape is much "simpler" than Adobe Illustrator.
15- BlueGriffon: Microsoft Expression is a popular option among those on the Windows desktop, but Linux users might be wondering what the closest thing to it would be for them. Having looked at half a dozen different options, I've found that BlueGriffon is best suited for HTML5, has decent extensibility options and just generally provides a good new-user experience.
The only real issue I found with this Expression alternative is that it's still very young. Just make sure to update often and grow with the project for best results.