The main one I use is called OwnCloud. The reason I like it so much is because it is an open source script that you can install on your own server, yet still access it with their app. I just find it to be more secure because I host the files and they just give me convenient access to them.
My favourite would have to be Chrome. It is just so comfortable and customisable.
My second favourite would have to be the TOR browser (works off of Firefox, I think) just because of the security it provides.