Definately grab a good used 400ex rear shock and some Ken O Connor bushings. You can get one for less than $ 50.00 on a good ebay day.
Like AWK said, used Works front shocks are a nice upgrade over stock and won't break the bank. If you have $$ to spend, custom Works or Elka shocks are nice but pricey. I'm not that heavy, either, at only 170 lbs, but I love my Works front shocks. I used to hit a bump and would feel it pretty good. Now, with the Works, its "what bump!?" Lol.