My favorite California wine region tends to be the Santa Rita Hills area of Santa Barbra county, this is due my liking of Pinot Nior and Chardonnay. This area is only a 3-4 hour drive and makes for a great getaway weekend! Wineries that I am a member of include: Babcock, Foley, Gainey (Evans Ranch), Palamino.
In Temecula I would recommend Hart, Doffo, & Monte de Oro and only Reds – it’s just too hot in that valley to grow most of the white grapes.
I also agree with SDRealtor that you can find some great deals at several wine shops throughout the city. Bacchus on G downtown is a great example. They are very knowledgeable and will guide you to wines based on what you like.
