If you are using a android phone, then there are quite a lot of good free apps available.
This is one of my personal favorites, Very minimalistic, but has all the functions needed. I have stopped using Facebook (Desktop Version)
Quite good, but lacks functionalities compared to desktop version, but still good to connect with your professional network on the go.
Google Reader
A very good app and very close to the desktop version. Right & Left swipe are cool.
Evernote
A very good noting app. You can take Text as well as Voice notes.
Drop Box
File sharing app, Instant synching of files from different channels.
Gmail
Apps for Gmail Desktop version, The only disadbantages is you need to refreshing (Synching) to get the latest emails. But over all very good app. Sending email with attachments is super easy.
Angry Birds
Popular App for gaming. A very good stress buster. Time killer.