Trade secrets — the worst and the weakest
Halliburton managed to get audit reports of its Iraq expenses (including $108 million in overcharges) designated as confidential, and thus not subject to disclosure to reporters (or legislators).
DeCSS was originally claimed to be a trade secret.
EFF has a “patent busting project.” What are examples of the most unlikely and most abusive uses of the law of trade secrets? There's a story here.
Anything a company generates that is the subject of reasonable secrecy-maintaining efforts by the company (and that has economic value because it is secret) can be a trade secret. Things that aren't copyrightable or patentable may be trade secrets. Shh. I'd tell you what's going to happen next, but I can't — it's a secret.