This is a good starter list - http://lifehacker.com/5924212/lifehacker-pack-for-android-our-list-of-the-best-android-apps?tag=downloads
I'd suggest adding evernote, if like me, you have a number of different computers/tablets/smartphones/desktops/laptops on the go, and want to synchronize things.
I also second their recommendation of dropbox, for both PC and Phone.
I like coolreader for ebooks, because i've got it set up to download books from my calibre library, http://calibre-ebook.com/, a pc based ebook manager.
Can't forget the steam app, so you can see what your friends are playing, and if it's worth while to go to the server and play.
I like beautiful widgets on my phone as well, since i'm only running froyo, and don't have all the cool tools.