One of the better multi-vortex tornado specimens was captured on film by several chasers, with the seemingly best footage from Verne Carlson that shows 4-5 vortices within a larger tornadic circulation. You can get more information about this storm and about Verne’s chasing on his weather blog.
Skip to the 1:00 mark to watch the incredible dynamics at work!
For some reason there is no audio until 1:59, which is a shame. Still a great video, though!