These are five stories which don't feature popular ships and so might have flown under your radar. Give them a chance, because they're really worth reading!
1) Le Petit Mort (First Slayer/OFC; NC-17) by snogged - I realize that the First Slayer isn't the most well known of Buffyverse denizens, but this ficlet features her in the most intriguing way. An angsty-sexy take on the beginnings of a primal battle that will surely satisfy.
2) Frankenstein (the Without Pity Remix) (Adam/Oz; NC-17) by snowpuppies: I have to warn you that this is incredibly dark, but if dark is your thing... it doesn't get darker than this. Snowy takes Oz to a Hell beyond imagining and gives us an Adam who, if he'd been shown like this in canon, would have easily taken his place at the top of the Big Bad food chain. This is a symphony of exquisite brutality.
3) And Your Enemies Closer (the Ten Things Connor Learned About Fred Remix) (Connor, Fred; G) by aadler: I am not a fan of Connor, but this story really made him intriguing to me. This take on Connor's relationship with Fred and on the way he sees the world brings him to (detached) life and offers a compelling portrait of someone who almost sees... almost.
4) And It's All Over But The Shouting (Cordelia, Oz; PG-13) by tiny_white_hats: This is a very poignant tale of Oz and Cordelia forging a fragile friendship in the aftermath of the 'fluke'. Truly excellent.
5) Memory } Recall (Tara/Buffy; R) by snowpuppies: A tale intriguing in both form and content. Tara and Buffy in the wake of Tabula Rasa. 500 words of wonder.