I'd go with Chrome over Firefox, personal preference. The majority of browsers today, even the new IE, leave the same effective footprint on your computer (differences are negligible). The reason for my choice of Chrome is I like the interface it has of the other browsers and I use many other Google products so they play well together (Calendar, Tasks, Docs, Google+, Maps, Latitude, Voice, Analytics)
If you plan on dealing with .docx, .pptx, .xlsx, etc. documents then install MS Office. Otherwise it's a waste of space.
Skype/Dropbox/VLC/Audacity/TeamSpeak/mIRC/JMP/Steam all have negligible footprints and you should get them if you plan to use them.
For virus protection I recommend Microsoft Security Essentials. It's free, made by Microsoft for Windows, and it's not too heavy or invasive.
True SL viewer (non-text based, etc) is based on personal preference, they all have the same effective footprint (differences negligible).
VLC player is a good choice of media player because it supports a wide range of codecs all in one easy package.
As for PS2, it will be a heavy footprint but none of the above software I mentioned will affect its performance on your computer (if it does there's something wrong).
Matlab/Mathematica/Solidworks/Photoshop will have heavy footprints, only install if you plan on using them.
I hope this helps.