Here are some.

Beautiful Mistakes. by Spikes_slayer08
http://dark-solace.org/elysian/viewuser.php?uid=981Runner up for Best WIP at the Cradle of humanity awards.
Buffy and Spike have been best friends for as long as they both can remember. After one passion filled night together Buffy and Spike find themselves in uncharted waters. Cheating partners, a bottle of Jack Daniels, tight shirts, jeans and entangled limbs. Was the night all one big mistake? Will Spike realise Buffy's true feelings before he looses her forever? or will it all just be to little to late? Complete
Keeping Secrets by Spikes_slayer08
http://dark-solace.org/elysian/viewstory.php?sid=2831&ageconsent=okArmed with fake I.D's 16 year old Elizabeth Buffy Summers and her best friend Cordeila Giles head out to L.A's hottest club intending on meeting up with Cordy's older, secret boyfriend Xander but when Cordy and Xander bail on Buffy she meets the man of her dreams Spike. He is everything she has ever wanted in a guy fun, smart, sexy, and a wonderful lover only problem is he is 22 year old collage student and thinks she is the same not a 16 year old high school student.How will Spike react when he discovers the truth? will he be able to forgive her? will he be able to put her age aside? and is her age the only secret she is keeping from him? Complete
http://dark-solace.org/elysian/viewuser.php?uid=23Guilty Pleasures by Ashlee
When William 'Spike' Bradley accepts a teaching position at Sunnydale High School, the last thing he expected was to meet the woman of his dreams. Especially considering the woman in question is his student. Complete
This fic has a little bit of everything and is very long. It's still WIP.
Unexpected Series by Passion4Spike
http://dark-solace.org/elysian/series.php?seriesid=90Summary: This story picks up at the end of Season 2, The Becoming 2. Buffy has made a deal with Spike to defeat Angelus. It goes off canon when Buffy leaves Giles' flat after talking with Whistler about how to defeat Angelus. Will Spike still help Buffy defeat Angelus when things go pear shaped? And what then? Where will their lives go from there?
You'll find familiar challenges for Buffy with unexpected results as Spike faces them with her. If you like a story with love, romance, sex, fights, angst, tears, laughter, marriage and babies then you're in the right place! I hope you enjoy it!
Runner up for: Best AU, Best Romance, Best Characaterization (Spike) in the Sunnydale Memorial Fanfiction Awards, Round 21
This one is still WIP but very long already.
Origins by Niamh
http://dark-solace.org/elysian/series.php?seriesid=66Post Season 5, veers from Canon, but uses elements that were seemingly left discarded by the writers.
This fic has a little bit of everything and is classic.
Love Bunnies aka The Bunnyverse by NautiBitz
http://dark-solace.org/elysian/series.php?seriesid=75The series/saga that jumped off from a sweet (and naughty) little story about Spike and Buffy being rabbits for a night. Not as "fluffy" as it seems...
Began as the one-shot "A Bunny In the Oven", originally published in 2001. That became the lengthy series, "Heart Don't Lie", which was completed in 2007. Followed by the sequel "At It Like Rabbits", completed in 2008, and tied up with the PWP one-shot "Baby Likes to Roleplay", published in 2009.
Collectively, this series has won thirteen awards, including "Best Series", "Best Romance", "Best Smut", "Best Work In Progress", "Best Lighthearted", "Best Long Fiction" and "Best Baby Fic" from various awards sites. Complete