King M Idas was himself a Zillion Dollar Bill, since everything he touched turned into gold, Unfortunately that included food, so he had to beg for the wish to be rescinded before he starved to death. He also had to beg the gods to restore the transformed golden objects to normal, thus losing all the money he'd gained, because one of them was his daughter.
The Goon Show often included plots revolving around very valuable items which turned out to be worthless or just got their owners into trouble. These included a million-pound inheritance which Neddie Seagoon couldn't spend until was 100 years old, a treasure map which the characters spent the entire episode bribing each other with smaller and smaller portions of, another treasure map tattooed on a set of false teeth leading to the tomb of Genghis Khan, and the phonograph cylinder in "Tales Of Old Dartmoor". This was a particularly notable example as the treasure was buried under the floor of Britain's most secure prison, making it very hard to get to. The convoluted plan to achieve this naturally ended in total disaster.
The Portrait of Madison in "The Long Goodbye" wasn't impossible to spend because nobody could make change. The problem was that it was part of a much larger sum stolen from the local equivalent of Tony Soprano, and since there were so few in circulation, he would know that anyone in LA seen with such a thing likely had something to do with the robbery. This does indeed get the hero into a very sticky situation.
In the Ealing comedy "The Man In The White Suit", the hero invents a chemical formula for a synthetic fabric with will never get dirty or wear out. Unfortunately, instead if bringing him the expected fame and fortune, it angers everyone in the clothing industry from the bosses who will lose their profits to the workers who will lose their jobs, and he is pursued by a howling mob, his prototype suit ironically making him more conspicuous. Luckily, this being a comedy, nothing bad happens because the formula was worthless all along.
But the ultimate Zillion Pound Note has to be the title object from the book and film "The Maltese Falcon", which will bring vast riches to its owner, or rather, it would if it were the real one, which of course it isn't.
See also the original version of "Bedazzled", in which George Spigot (actually Satan) offers the hapless Stanley Moon seven wishes. Not yet believing that this peculiar person is really the Devil, Stanley requests an ice-lolly. He is taken to a shop where the Devil is about to buy the lolly, but produces a million pound note (or what he claims is one) and asks Stanley to pay for it himself because he has no change. This turns out to be the Devil's cunning plan to grant the first wish so unimpressively that Stanley doesn't notice that he's had a wish granted at all, so that when he inevitably makes a mess of things and tries to use the last wish to fix everything, he will have already run out and be stuck in a disastrous situation.
Diamonds can now be manufactured using a technology that's essentially a superpowered pressure cooker. The diamond cartels are terrified that these might be seen as equivalent in value to natural diamonds, to the point that they now package the natural diamonds with written histories and even etch trademarks onto them. Thus far it's working, as most people will see the manufactured ones as inferior (unless they're very familiar with tales of Blood Diamonds).
This is completely untrue, and bugs me a great deal. The "Diamond Cartels" (Read: De Beers) own the process of making synthetic diamonds, and do all the manufacturing themselves. They're hardly terrified, synthetic diamonds have been around for over 50 years now, and have not exactly decimated the diamond industry. Synthetic rubies and sapphires are Older Than Television, and have had no effect on the price of those stones, either. Cultured Pearls did manage to affect natural pearls. . . by making them more valuable.
Somebody's posted bad information on Synthetic Diamonds in several tropes and I'm in a good position, being a professional in the Industry, to correct this with facts. I want to remove the false information and correct it, but I'm not sure of the exact protocol. Do I just delete it or do I add a comment underneath countering the wrong information? I've seen both done in various tropes and don't want to make a misstep. Tried to post this question in Trope Repair Shop but the forum's full and won't allow new threads.