The reason people read SF is for the ideas.
I've read a bunch of short story anthologies, best of the year stuff. Often I'll remember one amazing idea, but won't remember the story. Here are the great SF memories I have which I'm looking for the origin of.
An episodic story of humans gradually evolving during a thousand year long war with an alien species. First their giant ships divide into classes, and eventually the classes diverge genetically and culturally as well. Instead of being generalists, humans become instinctual - pilots have their sex drives linked to guiding missiles, etc. Eventually none of the beings actually know what's happening or why. Amazing story.
someone buys a super-version of sim-earth and gets really into it, setting up conditions for life, watching it develop, learning the languages that his race invents, being worshipped by the people, and eventually entering the world as one of them. Incredible.
a trombonist discovers a simple way to duplicate any object. He dupes his trombone and sells it, and buys some other instruments. Then he dupes himself and creates a band. Eventually there are hundreds of him running around, then millions, then a huge war. Turns out that duplication isn't quite perfect, and introduces slight changes. So he sees many versions of himself. Eventually they all die out and he goes back to his poor life. Update: this is actually a story by William Tenn.
A species with 4 sexes reproduces by taking any group of 3 and "wurpling", which produces a being of the 4th sex. There is usually one sex which is more common, and looked down upon - nobody wants to mate with them, which perpetuates there being too many of that sex. Since the 4 types have distinct personalities, the population goes through drastic sex-balance shifts. Update: This is actually by Frank Herbert, and doesn't really hold up upon re-reading.
A extreme sports lady tries the ultimate trip - getting merged with a synthetic life form which drills your brain and combines with your neurons, while you are floating inside it, in space around the rings of jupiter, photosynthesizing, in the middle of a 3-way population war. I think this one is called "equinox". while floating among the rings, she meets various interesting characters, including her quintuplets which she was forced to bear while living in one of the ring cults, who telepathically picked up on her joking notion to name them army, navy, air force, marines, and coastguard while they were in her womb, and have been looking for her. Update: This is a story by John Varley.
A depressed suburban man bumps into a silvery alien blob who likes to envelop him and communicate. He likes this a lot. Turns out the blob isn't in love with him after all, but only looking for info on Earth, and sees other men when he's at work.
On a primitive planet, botanists ride giant motile lily pads, controlling their direction with low intensity lasers. One day, the pads don't respond as expected.
A man slowly emerges from what turns out to have been a self-imposed exile on Earth. He had hypnotized himself into become a normal IQ 100 human, but gradually wakes into his true self, a galactic spy with a four-digit IQ, just as his false identity is being discovered by other super brainiacs.
One morning the elevator boy surprises the professor with insights, borrows a calc book, starts reading. Prof feels pretty inspired himself. Pretty soon it's going on all over the world - turns out every X million years, the Earth passes through a band of dumbness in space that slows down our brains and causes extinctions. Coming out of the band, humans become insanely smart, and peace mostly prevails (except for a few darn conservatives), until everyone leaves Earth for better things. Left behind are an incredibly retarded guy and a collie, now of about equal intelligence. They make do.
First contacters exploring a really nice planet discover a super awesome natural predator bear-thing that's practically unkillable, and intelligent as well. They invent a drug which makes this predator drunk, and imprison most of them in a thorny enclosure. Drunken bears occasionally escape, wreak havoc, and try to sober up and figure out what's happening to them.
A stowaway on a tiny landing pod is discovered during approach to a planet. Due to mass considerations, there's simply no way that either one of the occupants of the pod can survive atmospheric braking unless the stowaway is thrown out of the ship. Update: It's a story by Tom Godwin.
First contacters find extremely advanced but abandoned ancient cities, and small tribes living in tiny huts in their shadow. Turns out the tribes aren't so primitive after all. Update: This is "Forgetfulness" by Don A Stewart.
A kid discovers alien tourists in suburbia. He finds a ring of invisibility which makes you blind because your eyes don't grab any light. However, the ring only makes you invisible human-visual light, which is ok for aliens, since they can see in IR and UV. There's a nice scene where he steals a UFO, and imagines he's quite good at flying it, cause he never bumps into anything. But it turns out the UFO just won't let itself be crashed.