Various examples that aren't allowed: EULAs that purport to prohibit resale of books (first-sale doctrine), labor agreements that purport to prohibit the employment of members not from the contracting labor organization (union closed shops), deed restrictions that purport to prohibit resale of property to a class of people ("no reselling this house to blacks"), noncompete agreements in some states, exclusivity contracts entered into from a position of market dominance (the Microsoft and Intel OEM cases), certain kinds of explicit tying even when not in a position of market dominance, bequests that contain ongoing conditions on the heirs' behavior (rule against perpetuities), etc.
One example that is also in the "seems related" area but is legal in the U.S.: resale price maintenance, where a manufacturer can prohibit a retailer from selling a product below a certain price. One that's currently being debated is the vague set of issues around "network neutrality", related but not identical to the last generation's debate over "common carrier" status. Gray area: EULAs that purport to prohibit decompilation and reverse engineering.
I know it's a category with vague edges, but it seems like there should be some name for it? These kinds of contracts, even the ones we decide are allowed, seem different in kind from pure exchange contracts of the form, "I give you $100, and you agree to provide me with 2 hours of consulting".
The thing is that, as you say as I understand it, whether a contract is considered unconscionable is normally a complex question; for example, terms that are unconscious in a residential real estate contract can be included in a commercial real estate contract because a commercial renter is considered more sophisticated (and so if you rent commercially, you better be sophisticated and count your fingers after every hand shake). One guiding question is whether the signer really knows what he getting into.
By that token also, I believe a number of terms are considered unconscionable if you click through them on a website. I would speculate that if a vendor sent an actual devil who blew smoke out his ears and demanded a video-taped signing in blood celemony, that vendor would have a stronger claim that "the signer knew exactly what he was getting into".
Will Apple employ Devils in the future? I think Microsoft may have them all tied up...
IANAL of course...