to be honest, only you can know what the programs you need are.
But as a base I always install
An office package (openoffice or MS office)
A PDF reader (foxit)
Flash player
Malarebytes (good to keep your system free of spyware)
Anti-vrius
irfanview (a picture viewer)
VLC player (media player)
(sure I've forgotten a couple LOL)
The above should be enough to deal with most common file formats you are likely to come across. But it's not quite as simple as that as you'll also have a lot of eee pc utilities installed which although not strictly speaking needed they do add to the functionality of the netbook (improve power saving and so on)
you can definitely remove anything that says it's a toolbar though :)
Other than that your best bet is to go through each item in turn, type the name of it into google and see what it says it is and if it's a required item or not. (but keep in mind what I said in the first sentence, just because others don't need it or use it doesn't mean you don't)