Perfect World by Cousinjean
http://www.allaboutspike.com/fic.html?id=96 R, post-Grave. Spike wishes that he "never got the bleeding chip in the first place," - and discovers the world dominated by Adam and his minions, where Giles, Gunn and Lindsey do underground work and chipped Buffy is kept in a cell for zombified Riley Finn's distraction.
Back Before Dawn by Annakovsky
http://www.fanfiction.net/s/1341554/1/ PG-13, post-First Date. What if Seasons 5-7 were all the fault of a vengeance demon and a thoughtless Willow? Think The Wish seen through the eyes of a Wishverse characters.
To Dream Again by Ariane
http://www.geocities.com/ariane_five/DreamAgain.html NC-17, post-Lovers Walk. “I wish Spike wasn’t a vampire. I could call the cops and get him arrested for breaking and entering. I’d never have to see him again!” Halfrek grants Buffy's wish and she discovers William. Giles finds the way to send him back to 1880, but it's too late: William has already fallen in love with Buffy. He decides to turn into a vampire to meet her again.
What You Wish For by
fer1213 http://fer1213.livejournal.com/178945.htmlhttp://fer1213.livejournal.com/179232.htmlhttp://fer1213.livejournal.com/179490.html Soft R. Post-Dead Things. Buffy meets Halfrek in Bronze and says fatal words "I wish it were okay--accepted, normal, whatever--for someone like me to be with someone like Spike". And Hallie grants her wish - VERBATIM. The next day Spike arrives at Buffy's birthday with Faith and they look very happy together...
It's Got To Be Perfect by
speakr2customrs http://www.speaker-to-customers.me.uk/buffyverse/igtbp1.htm PG-13 (I think), Post-OAFA. Buffy asks Halfrek to turn Spike into a perfect boyfried - human, soulful, caring, polite, but with vampire strength and sexual libido, with impeccable taste, good job, plenty of money, posh apartment and car - and no bad consequences! But, of course, every wish has a catch...