A build I personally enjoy in PvE:
Dagger Mastery 12 + 1 + 1
Curses 10
Critical Strikes 8 + 1
Mark of Pain|Black Spider Strike|Twisting Fangs|Black Lotus Strike|Death Blossom|Parasitic Bond|Optional Elite|Resurrection Signet
At the start of the battle cast PB on a few enemies to provide healing during the battle, the tank should round up agro while you do this.
Once agro has been established cast Mark of Pain on a central mob and execute your combo, dealing 200 AoE damage from the combo alone ( thus not counting MoP triggering from regular attacks ) and usually putting your main target near death.
Quite devastating
, and with an optional elite there are various options depending on personal preference.
Flashing Blades for protection
Moebius Strike for even more Death Blossoms
Locust's Fury for double strikes to trigger MoP even more.
Aura of Displacement for a quick shadow step.
Fox's Promise to make sure your combo isn't evaded or blocked.
Shattering Assault for enchantment removal.
Shadow Meld for a quick shadow step.
Wastrel's Collapse if you can find a use for it :P.