Yeah Evil Eye is awesome on Gengar when running a team with T-spikes support. And Venoshock is also amazing.
A poison stall mono team is definitely viable. Poison is mostly a defensive type anyways, in my opinion, resisting Fighting, Bug, Grass, and Poison... Sure, only one of those types is really absolutely common, but its still enough to pull through with. Plus, there are PLENTY of semi-defensive (or decently bulky) poison type pokemon: Nidoqueen, Weezing, Drapion, Garbodor, Amoongus, Tentacruel, and even the awkward Subsplit Gengar... Crobat even fits this description, running max HP, some speed ev's and the rest into Def and SpDef, he can take a hit or 2 and still Roost and U-turn.
Poison has so many choices to work with, and so much coverage, the synergy is actually very surprising.
@above: The ice team, at first thought makes me laugh because of overall frailty. But Honestly, any mono-Ice team works like any basic hail team. Looking that team over actually makes me want to try it out. Just that crippling weakness to common attacking type moves... fire, rock, fighting... terrifying.