Google for "what to install after installing Ubuntu".
Ombubuntu.co.uk does this list for every release of Ubuntu. As for my personal list, I'd recommend the codecs pack, vlc, chrome and sublime text. You might want to install wine for running windows apps and games.
Rest of what I install mostly pertains to my development related stuff (like git-core, vim etc). For listening to music i prefer Muzi, followed by things like youtube and grooveshark. For documents and stuff, instead of using libre office, I prefer using google docs, or just writing stuff in a txt editor in markdown. There are a lot of chrome apps and extensions that i use daily, but they are not specific to Linux.
Sent from my iPad