Try to stop in Geyserville to see Francis Ford Coppola's new winery (previously Chateau Souverain) for a glass of Sauv Blanc on their patio. It's lovely.

In the Russian River area, I second the motion to stop by Davis Bynum and Rochioli, they have great stuff. Also consider DeLoach and Hartford Family.

Up in the Dry Creek area, Ridge on Lytton Springs Rd has really excellent wines, and doesn't charge for the basic tasting flight.

Skip Simi, the winery's not that nice, and you can certainly do better on the wines.

Kimamom - good point on the tasting- isn't the Famous Gate terrific? It's one of the wine club shipments we most look forward to (unfortunately for our wallets we're in a lot of wine clubs!) :)