Let me add to the recommedations for the next lake over...
Not to knock Seneca, I just "remember" the Keuka ones better.
Jeebus, there are 40 wineries on Seneca now... wow.
I'll spare you that and hope someone else here knows them well.
But for Keueka/Hammandsport/Penn Yan.
-There is the afforementioned Bully Hill, I don't like their stuff, but, they've been around forever and it's worth checking out, at least for the tour.
-Then you have Dr. Konstantin Frank's Vinifera wine cellars. A bit snobby, but the bestr wine on the lake, period. Probably in the the whole finger lakes region. If you're going to Keuka, you have to go there, or you might as well not bother.
-Hunt Country- Worst wine on the lake... hahaha... but, by far the coolest people, very relaxed. Though they do have a kick ass vidal ice wine if that's your thing.
-Heron Hill- Don't remember much about their wines, but, its a cool facility, if a bit touristy. I think htey might have a Cabernet Franc that's not bad IIRC. (Look, decent Red is hard to come by up there)
-McGregor- If you must have Red, go here. The Grapes are imported, but, so what? It's good.
The reality is of course that you're going to get a lot of whites. Riesling, Gewurztraminer, Vignoles, Vidal, Seyval (uggh) and lots of others.... If they have Reds, they are Usually FA hybrids... sometimes they're ok, but, I've never heard the sentence come out of my mouth, "Oh, that De Chaunac is pretty good!" But, at the end of the day, when in Rome...
So, having said all that... the real jewel of Keuka Lake is this place...
http://www.villagetaverninn.com/index.php
If you can set it up to have lunch or dinner there, just do it. Thank me later.