a good rear shock

400ex or a trx/atc 250r shock. 400ex's are newer and probably the better upgrade, but you will have to get the bushing kit that someone sells on here to get it to fit properly. 250r shocks just need a little bit taken off of the top mount to get it to fit, and have a remote rezzy that will need to be mounted somewhere. Both are suppose to be good upgrades over stock.
 
I have the 400ex and it was a good upgrade with the stock swinger... very plush with the extended swinger :)
 
400ex or a trx/atc 250r shock. 400ex's are newer and probably the better upgrade, but you will have to get the bushing kit that someone sells on here to get it to fit properly. 250r shocks just need a little bit taken off of the top mount to get it to fit, and have a remote rezzy that will need to be mounted somewhere. Both are suppose to be good upgrades over stock.

i highly recomend oconner's bushings, they make it such a easy, fast job but you dont HAVE to have them. i found the correct size washers/nuts and welded them in.
 
This has been covered many times before, always use the search function first to find out what info may be listed in detail.

Also, a recent previous thread that may be of good use to you here:
400EX

Also, there is the cheap shocks sticky at the top of suspension section, good info there as well.