There is a dearth of performance parts available as bolt-ons for the LS. Magnaflow has some exhaust pieces, and there are replacement intake ducts/filters from several manufacturers.
The most cost effective add-on is undoubtedly a spray system. QuikLS has done a herculean effort to install an Eaton blower on his car---see his sticky-ed thread at the top of the screen.
For another path, see my 'Land Speed LS' thread in the HP section. It's moving much slower than I'd like, but I'm trying to get a business up and running.
You need to be an old-time-y hot rodder to make an LS fast.
KS