Grey Knights Rules:
Nemesis Force Sword: +1 to existing invulnerable saves.
Nemesis Force Halberd: +2 initiative (yes, this makes them I6!)
Nemesis Force Stave: Grants a 2+ invulnerable save versus close combat wounds.
All NFWs have Daemonbane: ignoring eternal warrior for daemons and psykers.
Brotherhood Banner: 25 points +1 attack to all models in the unit, and automatically pass force weapon pyschic tests.
Psybolt Ammo: gives +1 Strength to Stormbolters,Hurricane bolters,Heavy bolters, Auto Cannons and Assault cannons. (not worth +20pts even on a maxed out Storm Raven)
Psycannon: S7 AP4 Assault 2, Heavy 4, Rending.
Heavy Psycannon: S7 AP4 Large Blast, Rending.
Heavy Incinerator: Operates like the Hellhound’s Inferno cannon.
Nemesis Greatsword: S:6 allowing rerolls to hit and wound.
DK Daemonhammer: S:10 Thunderhammer.
Psilencer: R:24″ S:4 AP- Heavy 6 Gatling Psilencer has the same stats excepts it’s Heavy 12. Psilencers always wounds Daemons on a roll of a 4+ unless the score required to wound would normally be less.
Thanks to http://space-wolves-grey.blogspot.com/
ALL OUTTA BUBBLEGUM 
okay, but do nemissis swords ect count as powerweapons? because every grey knight has one so that would be anti-marine (chaos, codex, bloods, darks, templars, wolves and grey knights themselves)
Yep, each one packs a force weapon (power weapon). Which is great and does make them mean against MEQ armies. I wish they were better weaponskill and all didn’t come with power weapons. Letting you upgrade the ones you wanted to have power weapons. This would make units of them cheaper (and thus providing ‘wounds’ for the unit) while still nearly as deadly.