A sticky-post for 'My Immortal' - my novel-length crossover extravaganza about how Captain Jack Harkness became 'The Immortal' from 'The Girl in Question' (AtS 5.20). Canon compliant in the extreme! All individual chapters can be found in my Memories, but here's a breakdown story-by-story (click banners):
The main story, dealing with Jack's century+ exile on Earth. Including his enmity with Angelus, but mostly his relationship with Buffy. Ends before the start of S1 of Torchwood, but has spoilers up to (and including) 'Fragments'.
FitBs (complete stand-alones):
Very short. Deals with the battle in the alley.
Very long. What happened to Buffy & Co under the Master's rule?
Sequel. What happened next. Fits in around S2-3 of Torchwood canon.
I also wrote a very AU TGiQ crack-fic (AU from 'My Immortal' and canon, I mean), where Immortal!Jack decides to deliver the demon head in person. Because the world needs more Angel/Jack/Spike!
The Immortal's (sweet) Revenge. Summary: The Immortal has had enough of our darling vampires messing around and takes care of it in his own way. (Or: Capt. Jack pwns Spike & Angel. Concurrently.)
And look! I won something!!!