So, based on today's strip thanks to Oso's adventures, we know that Sheldon lives near the coast/beach.

Due to the type of trees drawn in the neighborhood, I'm more incline to say that he lives on the east coast - perhaps the coast along the Virginia or Carolina area?

That's an interesting question. Having just spent way too much time analyzing it, I have a different theory. First, I looked at the weather in Sheldon. I couldn't find any references to snow. Hail and freezing rain (11/18/03), sure, but no snow. Even when it's freezing out (1/27/04), background shrubbery looks full. Also, they are affected by weather patterns from the north (5/12/04), so they must live somewhat to the south.

Okay, combine that with their road trip, where they begin in the desert and drive through greener areas (7/9/05) on the way to the Grand Canyon. Then they hit Yellowstone, and finally Las Vegas, with only a day passing between Las Vegas and home.

This evidence leads me to believe that Dave has set Sheldon in the southwest, but in an area that's cooler than others, and has some lush forests. I'm going with his old stomping grounds of San Diego.

Hmm.
My guess: somewhere near Silicon Valley. You know, 'cause of Sheldonsoft.

 It's not too far from the ocean, I suppose.

I tend to think that Sheldon's home is a lot like Springfield on the Simpsons. It's as non-specific as it can be so that Sheldon can be as close or as far from any particular landmark that the story might need.