The very first Pratchett I read was The Light Fantastic:

I still consider it his best work, and one of my favorite books of all time, so ima gunna go off.

First, the book's title comes from the poem L'Allegro, written by John Milton in 1631:

Haste thee, nymph, and bring with thee

Jest and youthful Jollity

Quips and Cranks, and wanton Wiles

Nods, and Becks, and wreathed Smiles

Such as hang on Hebe's neck

And love to live in dimple sleek

Sport that wrinkled Care derides

And Laughter holding both his sides

Come and trip it as ye go

On the Light Fantastic toe.

Some of my favorite quotes from it in tribute:

The universe, they say, depended for its operation on the balance of four forces which they identified as charm, persuasion, uncertainty, and bloody-mindedness.

The Unseen University had never admitted women, muttering something about problems with the plumbing, but the real reason was an unspoken dread that if women were allowed to mess around with magic they would probably be embarrassingly good at it…

Greyhald Spold knows that Death is looking for him, and has spent many years designing an impregnable hiding place.

He has just set the complicated clockwork of the lock and shut the lid, lying back in the knowledge that here at last is the perfect defence against the most ultimate of all his enemies, although as yet he has not considered the important part that airholes must play in an enterprise of this kind.

And right beside him, very lose to his ear, a voice has just said:

"DARK IN HERE, ISN'T IT?”

“Well—how can I put it? When I wash a young man, carving my name in the world, well, then I liked my women red-haired and fiery.”

“Ah.”

“And then I grew a little older and for preference I looked for a woman with blonde hair and the glint of the world in her eye.”

“Oh? Yes?”

“But then I grew a little older again and I came to see the point of dark women of a sultry nature.”

He paused. Rincewind waited.

“And?” he said. “Then what? What is it that you look for in a woman now?”

Cohen turned one rheumy blue eye on him.

“Patience,” he said.

The short conversation that follows eventually led to a tree religion. Its tenet of faith was this: a tree that was a good tree and led a clean decent and upstanding life could be assured of a future life after death. If it was very good indeed it would eventually be reincarnated as five thousand rolls of lavatory paper.

When light encounters a strong magical field it loses all sense of urgency. It slows right down. And on the Discworld the magic was embarrassingly strong, which meant that the soft yellow light of dawn flowed over the sleeping landscape like the caress of a gentle lover or, as some would have it, like golden syrup.

Not for the first time she reflected that there were many drawbacks to being a swordswoman, not least of which was that men didn't take you seriously until you'd actually killed them, by which time it didn't really matter anyway.

“Inside every sane person there's a madman struggling to get out," said the shopkeeper. "That's what I've always thought. No one goes mad quicker than a totally sane person.”