USEFUL SOFTWARE | Free, Open Source, Commercial

[7heDubz]

Paint dot net for starters.

http://www.getpaint.net/index.html - Image and graphics editor | Free

Followed by the community codec pack (With Media Player Classic)

http://www.cccp-project.net/ - The Combined Community Codec Pack is a simple playback pack for Windows with the goal of supporting the majority of video formats in use today. | Free

EDIT - (OH Traggey already added CCCP I love it too!)

EDIT - (Oh.. and paint.net crap)

EDIT - Alright here. http://unity3d.com/ add that.