I vote for firefox - the number one - many nice extensions - like control many players(winamp, sonique and etc.) using the broser without have to open the windows of the program to control your musics. In my case winamp, i only left open the winamp agent and control the musics by the browser while i'm surfing in the web. Has many others nice extensions to control a lot of things without need extra programs to do something for you - like download controls and etc.
Ah yes, and can use skins too.
About mail client: I'm using thunderbird and is a great program too.
