In short, if I had to do it all over again, I would of gotten an IC first. It'* not a power adder, but it allows you to maximize your current mods and helps put less stress on the motor. (I'd also highly recommend the GM pump and INTENSE heat exchanger instead of the one'* that come with most kits..
Before I got the IC, the car was VERY sensitive to daily temp changes (i.e KR). With the IC, I get more consistent performance over a wider variety of weather. (It'* nice for it to be 90* degrees outside and I'm still able to punch it to pass someone without gobs of knock.)
To echo what Bill said, "Something else to consider is that increasing power is not necessarily about how small of a pulley you can run. As Todd from Intense has taught me, there can be a much greater increase in power from tuning and adding in timing than from adding more air by itself."
Once you start getting in beyond the basic mods (pulley, intake, t-stat) you should invest in a tuner. IMHO, cookie-cutter flashed PCMs sometimes hurt more than they help.
Just my 2 cents.
P.*. I'd also recommend a trans shift kit once you start increasing horsepower. It will help with prolonging the life of your stock trans.