Firefox
Opera
Iron
Popular browser by Mozilla
Another great browser
Fast browser based on Chromium code, but less data leakage than Google Chrome
Thunderbird
Lightning
Mail client by Mozilla
Calendar add-on
Microsoft Security Essentials
avast
Anti-virus
PDF XChange Viewer Fast PDF viewer and editor with many features
Open Office Alternative to Microsoft products
MyDefrag Way better than the Windows feature
VLC Player
Media Monkey
Winamp
Songbird
Fast and simple media player
Music manager and jukebox
Music player
Great music jukebox for PC, Android and iOS
Use FolderSync to sync your playlists to external USB drives (e.g. MP3 players)
Pidgin
Skype
Combines ICQ, MSN and other clients
Video-chat client
7zip Data compression, also deals with .zip and .rar formats
Paint.NET
Gimp
Image editors
CDBurnerXP CD and DVD burner
Dropbox
Microsoft SkyDrive
Data storage