I love BtVS crossovers, but have a hard time finding many good ones. This is a list of some of the best ones I think are out there.
If there's a title you think belongs here, e-mail me at sky_solo@hotmail.com; not all suggestions will be accepted.
Harry Potter
Harry Potter and the Key of Dagon by Don Sample
A chance meeting in London leads Dawn into a whole new world she hadn't suspected existed. This story takes place following Chosen and The Order of the Phoenix. PG-13
Twisting Time by Chelle
Harry and his friends are thrown back 120 years in time to victorian London. There they end up bumping into four well known vampires who are terrorizing the town... PG-13
Stars Not in Heaven by Water Mage
Lily and James Potter had another child years before Harry. Due to matters it was given up for adoption. Nineteen years later Buffy Summers finds adoption papers in her Mom's closet. Now Buffy is searching to find the family she never knew she had. PG
Star Trek
Stupid Portal by Tara Keezer.
Buffy and Spike get sucked into a 'verse not their own. Giles follows. Prophecy happens. R
Omphalos by Marcus Rowland
A Key comes out of the Wormhole... then things get weird... Deep Space Nine. PG
What if? Buffy Meets Star Trek by Johnny Snowball
The Scoobs and the crew of the Enterprise-E battle Evil in an epic rollercoaster ride of action and intrigue! A tale spanning the Galaxy- to new worlds and dark stations, can Buffy and Co help Picard's crew save the universe from one of his own? PG-13
X-men
Cairn by YLee Franklin
Buffy has discovered a distant cousin, who invites her to visit. His name? Scott Summers. Prophetic dreams. Two Summers in one place. TROUBLE! PG-13
Minutes to Memories by Bastille Kain
Logan gets a call from somebody out of his past that informs him the mother of his daughter just died. PG-13
Rocks on the Road by Bastille Kain
Hank Summers is framed for the murder of a controversial Senator while in New York. PG-13
Daddy Dearest by Rachelle Ryan
After more than 17 years of drug and alcohol induced vagueness what does Xander Harris' mother realize when she comes out of it? PG-13
Taking the Initiative by Dorian Blackthorne
When Professor Charles Xavier takes two of his students to a medical conference on the Mutant Phenomenon in Los Angeles, things take a turn into the unexpected. PG-13
Preludes to Heartbreak by Dorian Blackthorne
Follow-up to Taking the Initiative. Nicholas Graydon finds out more about the group behind the Initative, and what they're planning next. PG-13
Heartbreak: The Funeral of Buffy Summers by Dorian Blackthorne
After Buffy's sacrifice, heroes of all types gather in Sunnydale to say their final farewells. Decisions regarding the future will be made as the Scoobies, the crew of Angel Investigations, the X-Men, and VI face the realities of life without a slayer. PG-13
Batman
Things You Don't Want to Know by Reichenbach
After seeing her sister sacrifice herself to save the universe, Dawn Summers begins searching for her father and ends up getting unwanted help from the youngest member of the Bat Clan. PG-13
Buffy/Batman: Virtue by rbachman
Buffy & Batman team up to face The Joker & an ancient demon. PG
CSI
Due Diligence by Jeanny
A CSI x-over. The key to living with an evil hand? Keeping it occupied. R
Should Have Gone to Vegas by Marcus Rowland
When a mysterious corpse comes back to life, you know you're in a crossover with Angel... G
Manhunters by Marcus Rowland
Another mysterious death in Las Vegas; CSI investigate, but soon have to call for supernatural help. Crossover with CSI/BtVS/Angel, sequel to Should Have Gone To Vegas. G
Slayer Las Vegas by Marcus Rowland
Third story in the BtVS/Angel/CSI crossover series, sequel to Should Have Gone to Vegas and Manhunters. G
Miscellaneous
A New Path by Melissa Davis
A new slayer, goblins in Sunnydale, Vampires in the labyrinth, the Goblin King comming back into Sarah's life. Labyrinth Crossover. R
Double Destiny: Book I by Lisa Drexel
Buffy dies during a confrontation with Adam and discovers that she's Immortal and has been since since she drowned two years before. Story takes place ten years after events in Season Four. Highlander Crossover. R
Double Destiny: Book II by Lisa Drexel
Buffy dies during a confrontation with Adam and discovers that she's Immortal and has been since since she drowned two years before. Story takes place ten years after events in Season Four. In this book, the POVs change... Highlander Crossover. R
Distant Evil by rogue-angel82
Buffy the vampire slayer in middle earth. Lord of the Rings Crossover. R
The World With the Darkest Powers by Bayou Boy
Willow and Kennedy help the S.G.C. fight Annubus' new super soldiers. SG-1 Crossover. PG-13
New York Minute by Bastille Kain
Attempting to get back to her time, May Parker is pulled of course by the near apocalypse and winds up in Sunnydale. Spider Girl Crossover. PG-13
The Buffy Files by phoebenpiper
High school Buffy and friends are concerned when they hear two FBI agents are coming to town. But after meeting Agents Mulder and Scully, the gang is eager for them to stay. That is, until they start to receive portents of a new evil coming. X-Files Crossover. G
Family Issues by Marcus Rowland
An alien is missing somewhere in Sunnydale. The Men in Black investigate. Men In Black Crossover. PG