Have you consider a turbo or nitrous? Other than that there are companies that make stroker kits. You'd have to switch out everything including the crank, rods, pistons and cams.
Yeah, adding a supercharger is probably the most commonly added power adder - Vortech is pretty popular for the 99/01s. There's other brands too, just do your research on them first.
Also, try to avoid going over the 450 rwhp (at the wheels) mark. Not that it's a "magical" number or anything, but many others have seen the stock internal engine parts (ie - non-forged rods/pistons, etc) fail around or above that 450rwhp power level. If you want more power, do a proper build (added cost) before throwing big boost numbers at the engine.
Wouldn't hurt to get it tuned by a reputable tuner as well; should help with the reliability/longetivity.
Are you saying 450 at the flywheel or 450 at the rear wheels. It's very costly, but you can get in the 370 to 380 rear wheel hp which would put you at around the mid 400's at the flywheel. One way to get there are some built heads from livernois, stage 2 comp cam and a short runner intake manifold.