Copyright duration: another suggestion
OK, how about this:
You get 10 years copyright free of charge. If you want to extend it, go ahead, have another 10 years, that will be $1000 please (so I won't bother renewing all those poems I wrote for my wife). Not enough? No problem, extend from 20 to 30 years for a mere $10000 (and the majority of books drop into the public domain). Still not satisfied? At 30 years register for another 10 years for only $100000 (really popular authors only by now). To get from there to 50 years will cost you $1m (and JK Rowling - or her estate - and Disney Corp will probably consider it a bargain) and so on up.
This suggestion wasn't the result of hours of thought so you can probably point out a number of faults - the worldwide thing being the first that springs to mind - oh, and where should the money go? - but it does recognise that copyright has a monetary value and it stops publishing houses from holding back catalogues of books that they have no intention of ever doing anything with but that they're theirs so you can't have them.
I've been thinking books, mainly; I've no idea how this might work for music, movies, software, you name it.