I've been going the sleeper route. My PT Cruiser looks completely stock outside except for the antena coming out of the hood. Underneath, the body is shaved, it has the FNF upgrade, powdered graphite running gear lube job, I've got new batteries coming from that Able Battery place that was giving out free samples and just last night, I ordered suspension springs from QFM for independent suspension.
I love the sleeper idea, it looks like a regular old dumpy PT Cruiser on the outside, but underneath, its ready to rip.
See my sig for a summary