"And if every man on the shores of the Circle Sea had a mountain of gold of his own? Would that be a good thing? What would happen? Think carefully." Rincewind's brow furrowed. He thought. "We'd all be rich?" The way the temperature fell at his remark told him that it was not the correct one. (1.7.34-36)
As we see throughout The Color of Magic, gold grants a type of power to the owner. The Patrician isn't too thrilled with the idea of someone matching him on this power level, though. (Feel free to insert your own obligatory "Over 9000" reference here, dear Shmooper.)
In any case, Twoflower was delightedly taking picture after picture of people engaged in what he described as typical activities, and since a quarter-rhinu would subsequently change hands "for their trouble" a tail of bemused and happy nouveaux-riches was soon following him in case this madman exploded in a shower of gold. (1.12.2)
Twoflower's wealth gives him a Pied Piper type of power over people. In getting people to do what he wants them to, his power is oddly familiar to the Patrician's.
YOU DON'T HAVE TO TELL ME. THE WHOLE SYSTEM'S GOT SCREWED UP AGAIN, I CAN SEE THAT. LOOK, THERE'S NO CHANCE OF YOU—? (1.18.13)
You'd think Death would be the end-all, be-all of powerhouses, but this isn't the case. Even he is limited in his power thanks to a system that, like all systems, gets out of whack from time to time.
For a moment [Rincewind] thought Withel was going to spit him where he lay. But it was worse than that. He was waiting for him to get up. "I see you have a sword, wizard," he said quietly. "I suggest you rise, and we shall see how well you use it." (1.23.2-3)
Withel doesn't just want to kill Rincewind. He wants Rincewind to know he has the power of life-and-death over him. He craves this power because, as Ymor's second, he doesn't get to enjoy it as often as he'd like.
The Lady nodded slightly. She picked up the dice cup and held it as steady as a rock, yet all the gods could hear the three cubes rattling about inside. And then she sent them bouncing across the table. (2.Prologue.13)
The Lady's power can't be properly defined, and it's impossible to say when it will come into play. Oddly enough, that might make hers the most powerful power on the Disc.
The sword must have noticed him, too, because it suddenly spoke in a voice like a claw being scraped across glass. "Strange," it said. "Why can't he say eight?" EIGHT, Hate, ate said the echoes. There was the faintest of grinding noises, deep under the earth. (2.10.46-48)
The Color of Magic is full of examples of words having power, although this isn't always such a positive thing. Case in point: using the power of words to summon a creature with the nickname of the Soul Render.
But Time, having initially gone for the throat, was now setting out to complete the job. The boiling interface between decaying magic and ascendant entropy roared down the hill and overtook the galloping horse, whose riders, being themselves creatures of Time, completely failed to notice it. (2.10.129)
Okay, so maybe there is a power greater than the Lady's: entropy. Given enough time, even Bel-Shamharoth will fall victim.
Liessa bends her mind to the task of full visualization; above her in the musty air the dragons become fully visible, bronze scales dully reflecting the sunbeam shafts. Her mind throbs, but now that the Power is flowing fully she can, with barely a waver of concentration, think of other things. (3.7.2)
Imagination is also a super powerful force on the Disc, thanks to the fact that it exists in the physical world as octarine. This allows imagination to take physical shape in the form of magic and dragons. Super cool—depending on whose imagination we're talking about here.
"You have the Power!" "All I did was think of it." "That's what the Power is! Have I already told you that I am Greicha the First? Or is that next? I'm sorry, but I haven't had too much experience of transcendence. Anyway, yes—the Power. It summons dragons, you know." (3.13.60-62)
The other great thing about imagination being a power in the world is that no one has to be trained to use it. Twoflower was trained to not be imaginative, but his power of imagination is so powerful that he creates one of the best dragons ever.
[Tethis] stopped and stared intently at Rincewind. "Every night I come out here and look down," he finished, "and I never jump. Courage is hard to come by, here on the Edge." (4.4.6.)
The power of the unknown is terrifying, awe-inspiring, and difficult to full grasp. The Edge of the Discworld is a perfect symbol for the unknown, and it takes a certain kind of person to have the power to just jump into it (read: Twoflower).