In terms of gin, I'd recommend small batch or artisinal gin. Tanqueray and Bombay just don't seem to have the same depth of flavour (no offense to the previous poster's suggestions).
My personal recommendations:
Hendricks is a very popular top-shelf option. Great cucumber flavour.
Dillon's Unfiltered 22 is an interesting local option - a bit cloudy, very flavourful. Base alcohol is made from Niagara region grapes.
Death's Door again has great flavour, but the base alcohol is from hard wheat, so if your guests have gluten allergies it may pose an issue. (I didn't seem to react to it though) American made.
JR's Dry Organic is another great local option, made right here in Toronto. It's absolutely wonderful in a martini.
Victoria is another great Canadian gin, made in Victoria, BC. I find it to be a bit sweeter, with almost a coconut flavour. It's quite pleasant.
The Botanist is a personal favourite of mine. Not local, but the hand-harvested wild botanicals bring almost a kind of energy to the gin.
My 0.02. There's quite a few gins out there that I haven't had a chance to try yet, I'm looking forward to reading some responses from other gin lovers.