I have a Schwinn Varisty 700c 21 speed Hybrid bike (flatbar). I bought it at wal-mart for $200 about 6 months ago to commute back and forth to work. I have put about 300 miles on it so far and enjoy cycling more than i thought i would. I would like to buy a new bike (road) but cant really put up that kind of money right now for a new bike. But i can afford to do some upgrades on the bike to get through.
It is an aluminum frame with shimano quick shifters and a shimano tourney derailleur.

What upgrades do you guys recomend? (carbon seat post, carbon fork, better derailleur, ...)

thanks!