I recently had the need to extract a few dozen video clips from about a terrabyte of videocamera mp4 files (broken up into 3gb files), and went looking for a simple free tool that could load the videos and help me extract smaller clips from them in an easy manner.
I thought it was worth a post for others who may one day find themselves needing the same type of tool.
The one i ended up using is the free (open source) Avidemux: http://fixounet.free.fr/avidemux/
It has a very clean minimalist user interface, is fast, and does a great job of letting you select regions to extract and save.
Not perfect, but highly recommended if this is the kind of thing you need to do.