I've heard the theory that a NATO submarine was playing hide-n'-seek with the Russians when they collided. During the Cold War, this was a popular method of testing equipment and seeing who was the best to go silent in the water. I'm sure the Russians and the Western Nations still play games like that. That NATO-sub was later to have been seen at docks in Norway, being repaired.
I'm not really prepared to believe such a theory though, and go with the official one - that it was indeed an accident - however interesting these conspiracy theories are.
Cheers.