A concept that I'm looking forward to translating to the new Dark Angels codex in the near future (... as a chaos / fallen counts-as -- remember that those grey knights are evil sorcerers, no really, they are sorcerers...). The idea is to blend Death Wing with some of my favourite Grey Knights entries (particularly Mordrak and his ghost knights) and exploit the best sides of both styles of terminator armies. Without tanks, the idea is to either deep strike in (particularly the Dark Angels detachment) or actually start out on foot. Choice selection of the powers of the librarian can help here (e.g. the summoning). The main issue is flyers ... might have to swap out a squad for some storm ravens (etc.) as a counter. Not ideal, but necessary now for 6th edition!
1850 points, 33 models, no tanks:
Grey Knights (Primary Detachment):
Mordrak (200 points)
4 Ghost Knights with halberds and hammers (160 points)
Librarian with 2 extra powers (160 points)
Grey Knight Terminator Squad, 6 models (240 points)
Grey Knight Terminator Squad, 5 models, psycannon (225 points)
Dark Angels (Allies):
Belial with thunder hammer and storm shield (130 points)
Death Wing Terminators, company banner, apothecary, 4 thunder hammer & storm shield, 1 heavy flamer plus chainfist (280 points)
Death Wing Terminators, cyclone missile launcher, 1 chainfist (240 points)
Death Wing Terminators, 3 thunder hammer and storm shields, 2 paired lightning claws (215 points)
(NB: Death Wing Terminators count as either Troops or Elites with Belial in the army list ... hence no violation of allies rules here before someone mentions it!).