What kind of performance upgrades can I do with my 98 park avenue that has the 3800 series 2 engine without adding a supercharger

The real weak area with a car like yours would be handling. I would look at changing springs, shocks/struts, tires and wheels and maybe adding heavier anti-sway bars. A cold air intake and performance exhaust will pick a few HP but don't expect too much.

Here is a specialty forum for your engine - http://www.3800pro.com/forum/

Any sugestions on the intake and exhaust? what about performance modules

More goodies - http://zzperformance.com/3800/engine.html

A lot of great info on your engine -- http://www.enginebuildermag.com/2008/03/rebuilding-the-3-8l-buick- engine/