How long is the video, what format and file size ?
I don't know anything free that will do it. That doesn't mean there isn't any, just I don't know of any.
It can be done in Adobe Premiere Pro 1.5, (definitely not free) but on the basis that the video image isn't likely to be square, any video which is shot other than the right way up or upside down is probably going to end up looking wrong, possibly with black bands on the left and right sides of the picture. These can be got rid of by expanding the video, but the upper and lower parts of the original video would be lost.
I just tested the theory with a JVC camcorder to see what sideways footage would look like when rotated and expanded to get rid of the black bands
Original
Rotated
(just rotating it loses the 'top' and 'bottom' of the image)
Expanded
(getting rid of the bands enlarges the images and it loses
even more from the edges)
The other way to do it would be to rotate it and then shrink it so the whole of the video image is viewable, but it would end up slightly smaller than it would have originally been.