Though I haven't been yet myself, I've heard good things about The Falls (1604 Kelly Ave.), the fairly new cafe, eatery and wine bar in Mount Washington.
The Falls serves wines by the bottle, pour or half-pour. It's the last option that I like the most.
Half-pours let you taste a variety of wines without putting spots on your liver. They don't cost that much either.
For example, a typical pour of sauvignon blanc at The Falls might run you $5, but a half-pour will only be $3. Unlike many area wine bars, The Falls offers all of their wines by the half-pour.
And judging by the photo, these are some pretty hefty half-pours.
The only other time I've come close to a half pour was a couple years ago at Cinghiale, when Amie ordered a half-pour, only to receive a regular pour. The restaurant only charged us for a half-pour, and Amie gladly enjoyed the extra few ounces of wine.
(Photo by Midnight Sunner CJ)