Two more good stories I found, one for each show:
The Doctor arrives in LA, 1997 and sense that someone’s been playing around with timelines. It’s a neat story based around Dawn’s insertion into Buffy’s timeline, which is an idea that makes huge sense for a Doctor Who crossover to deal with.
Spike finds Cardiff under Harmony’s desk. It’s a fun fic (look at the character list) with a dark edge, because Torchwood are five years in the future and Angel’s team don’t seem to exist any more.