1 - Video
The Chinese Based SPlayer is one of the best Free Video Player out there. It can handle anything you through at it and GPU Accerlation mean it won't bog Down your PC.
If you don't like the interface of SPlayer, the Best Alternate IMO is the KMPlayer. Runs Everything and is one of the most Feature rich Player.
2 - Compression
A Compression Tool is a must have now a days. Haozip is the best Free tool for compresion i have seen. Way better than Winrar, 7-Zip, Peazip etc and oh! You don't feel like your using a 98 software on a 2011 PC.
3 - Torrent
I don't really hav to explain this one. You know what it does, and if you don't, nevermind....
4 - Antivirus
Microsoft Security Essentials:-
Though most of you will say AVG Free or Avast personal is better than MSE but trust me this one is the Best. Have tried all of them and at the end MSE is the simplest and provide best Intigration with Windows. And you can forget you even have this after installation.
5 - PDF Reader
Foxit Reader :-
Foxit Reader is my personal Fav. Much lighter on the system than the Adobe Readoer.