Best bangs for the buck - get a new air intake tube/filter (K&N, Volant, Pacesetter, Airaid, and Rusty's all make 'em). Rusty's is the cheapest. Then get a Borla catback system, to replace the restrictive muffler/tailpipe. That's good for 10-20HP. Skip the TB spacers and other gizmos. If you want a few more ponies, add the Borla headers and get the Hypertech programmer. That's about it, unless you want to swap out for a $3400 4.6L 260HP stroker block.