A list complied by a Taleworlds forum user link here: http://forums.taleworlds.com/index.php/topic,230124.0.html and the actual threads are here: http://forums.taleworlds.com/index.php/board,283.0.html
Joining a active regiment(fancy name for clan) will enable you to join in on the majority of the community's events as oppose to joining in the very few for non-regimental players as a public regiment. Also, there would most likely weekly training sessions imposed once you're in a regiment; this will either bore you and or make you a better player, really depends on the regiment. Overall, both types of regiments can help you see some organized play in Napoleonic Wars , but being in an actual regiment will allow you to be in more.
Community events: http://forums.taleworlds.com/index.php/topic,222722.0.html
Here I will embed two videos of a public reg and one example of an actual reg.