Fin Amour, by angearia
AU S5; Spike/Buffy
Not the first Buffy-is-pregnant-with-the-Key fic I've read but almost certainly my favorite, this has occasionally humorous, eventually gorgeous Spuffy stuff going on in it, plus a three-hankie angst warning. Really lovely and on my list of Favoritest Babyfics Ever.
Let Nothing You Dismay, by constance_b
In this old-school fic, Buffy gets nabbed by Initiative-type bad guys, and it's up to Spike and Dawn to save her. Too bad Spike has to get his chip out to do it, and too bad he doesn't have snowball's chance of getting her to trust him. Weird to say, but my favorite bit here is the epilogue, which I think I've read at least twice as many times as I've read the rest of the fic.
I, Robot, by calove
Another classic that I somehow missed. Giles and the Scoobies order a Spikebot for Buffy for training purposes. Surprisingly, this results in much less porn than one would expect and many more sweet character moments of Buffy and Spike, together and separate. (Also: Spikebot/Buffybot, the match made in Warren's basement. The hijinks they could get up to, if only Spikebot were anatomically correct!)
Apologies: A Dialogue, by willowgreen
By magical means unspecified, Spike and Buffy are made to actually talk out all the things they're sorry for. The author apologizes for the meta nature of the fic, but honestly, I love seeing these two get all their issues out in the open. Basically a sweet, lovely fic despite the subject matter.
Obstacles, by shapinglight
An oldie-but-goodie that I read long ago and have been cogitating on all this time. In a happy Spuffy future, Buffy's sudden loss of her powers throws huge tension into her life and her relationship with Spike. Despite the Spuffy nature, what's stuck with me most strongly about this fic is how Buffy comes to terms and deals with her, ah, handicap. It's one of the first fics that started me on the path to understanding the hero that is Buffy Summers.
The Other Stuff
Taking Care of Business, by brutti_ma_buoni
post-NFA; Faith, Wesley, Illyria
After it all, Faith comes to clean up some loose ends at W&H, specifically Wesley, who appears to be alive when he's supposed to be dead. Some great lines, some lovely character interaction, a beheading or two, a conclusion that fits perfectly even when you wish it didn't.
Courting Sin, by leni_ba
S2 AU; Buffy/Angelus
I'm really only interested in Buffy/Angel in S2, and then only because of the way it subverts any number of romantic and horror tropes. Buffy/Angel happily ever after does nothing for me. However, I seem to have a weakness for twisted dark manipulative Buffy/Angelus, of which I'd be unaware were it not for this fic. Claustrophobic and brooding, with a narrative style that skates on the edge of traditional, this is a really impressive example of the sort of thing it is. Highly recommended for those who think they might like that sort of thing.
Battlefield of the Gods, by bobthemole
post-series AU; Glory, Illyria
Two old acquaintances of the multi-dimensional pantheon get together for coffee. Humor and Glory!pwnage ensues, as it should. Delightful.
Wide and Starry Sky, by brutti_ma_buoni
A companion piece to the Rulesverse Spuffy babyfic Winds Blowing Chill, this is about Wes and Illyria working towards something that might possibly be a relationship, and I think it's the fic that started me shipping them in the first place. Plus it's got Illyria leaving a message on an answering machine, which is difficult to beat for sheer fabulousness.
Silence Speaks, by knifeedgefic
The beginning of what the author says will be an ongoing series of Dru-centered ficlets, these first few are fascinating and chewy, with some very sharply written imagery. I'm always interested in fic about Dru, and these are very satisfying indeed.