There are a lot of options for the different types of software we are used to. GIMP is the Photoshop one, but you know about that, the new version which you can get but isn't official is really amazing. If you have need for an Adobe Illustrator replacement there is Inkscape, which is awesome, I actually prefer it.
For RAW Processing and or variants like Lightroom/Aperture that do other stuff like organization, selective non-destructive editing and handling a lot of files at once... there are too many options to mention. A few I know off the top of my head and in absolutely no particular order: Raw Therapy, Darktable, UFRaw, F-Spot and the list goes on. For video editing, FX and nodal based compositing as well as 3D animation, all are actually done quite well in one software called Blender, but it's less known that it even has Video features in it, but it does and they are pretty awesome. There are too many too mention for various sound and music editing and composing needs and it's not my field but for the video guys who need to edit sound and music, there is no shortage.
Once I get a really nice combination that works well and should work on everyone's computer I'll either make a list or it could actually be released as a custom distro because it's all open source and is legal to share custom tailored versions of the entire operating system/software/settings/etc. that is ready to install. If you want to start testing it's fairly easy to install a virtual machine on top of your windows or osx installation and just test the waters, running linux as if it were an OSX application or a windows app, and then you can see what it's like before making the full jump. Private message me if you want, I know a little but I am still learning the new environment and have a ways to go, but if I can help I will.