The only ones that I've read were collected in Ombius Volume 1
, all of which I thought were pretty good. "The Origin" is especially fun, as it was intended to more accurately reflect Joss's original movie script than the filmed movie did*. "Slayer, Interrupted" calls back to season 6's "Normal Again," by featuring Buffy in a mental asylum shortly before the move from LA to Sunnydale. "All's Fair" was a fun Spike and Drusilla story at the 1933 World's Fair.
(* Joss has even referred to this one as being "pretty much" canon.)