with most electric speed controllers (ESCs) they burn out and die if you put the polarity the rong way round , try not to do this as ESCs are expensive. I wouldn't by duel ESCs because If you burn out 1 side you destroy the whole thing, so I would get 2 seperate ESCs.
I use these's
http://www.technobotsonline.com/syren-2 ... oller.html
because they are programmable and have a peak current rating of 45A which are achievable for a few seconds.