In 2001, I came down the coast to Oceanside and then linked up with Southern Tier bicycle route that went via Phoenix. Journal pages at: http://www.mvermeulen.com/oneyear/usa.htm It was a pretty straightforward and nice ride.

In 2000, I came from San Jose via Bakersfield and then further across via Death Valley to Las Vegas. The crossing from Bakersfield via Kernsville was a nice way to cut across, though I haven't worked out exactly what you would do after that: http://www.mvermeulen.com/vegas/index.htm

It depends a little on time of the year, but my own preference would be more towards sticking down the coast first and making the crossing further down and hence most like the first route I posted above.