Oh man, SO MANY FIC RECS. Uh. Basically, I would recommend anything from the entirety of my flist. Especially snickfic, angearia, diamondtook862, ghostyouknow27 and penny_lane_42 for Spike/Buffy.

For Angel/Cordelia, samsom and anythingbutgrey are my go-to guys. The latter also writes excellent Wes/Lilah.

The world is extremely lacking in Angel/Faith, Angel/Darla, and Wes/Faith fic, I'm afraid. Though, superkappa recently wrote this Wes/Faith beauty for me, if you're interested.

As for VMars comms--well, there is veronicamarsfic.