X2 with Josh, get on Rockymountain atv and look for a chain and sprockets. As for a chain brand a prefer and personally run a Regina chain. Primary Drive brand sprockets are nice, and not too expensive.
Exhaust wise for good all around riding I would get Pro Circuit pipes. They have great low end power and will pull hard all the way to full throttle. Everyone has there own opinion on exhaust, and any aftermarket exhaust is going to be a huge improvement over stock. Just remember to rejet after you change the exhaust...more air flow, the bike will need larger jets for more fuel.