There is a ton of stuff you can do to the regal. I have a 99 regal GS myself.
Check out
RegalGS.org, great place to learn about modding your regal.
To answer you question about suspension, KYB GR2 or the KYB AGX with SSC springs are the most popular suspension choices, but are pretty pricey, but its the proper way to have it done.
Our cars aren't listen in many places for perfomance mods, but looks up grand prix performance mods since they are a W body are well with the same engine and frame.