Offhand I can't think of any good free ones that are both easy to use and frame accurate.
But, you can get one of the very few frame accurate editors on a 30 unlimited trial here:
http://www.womble.com/download/
Or, if you want an even simpler to use interface, but less powerful - no real effects in this one, but great for simply stitching things together:
http://www.womble.com/download/vcr.html
The trials are 30 days, unlimited (no watermarking, no cut off after X many minutes of editing, etc)