There are many California bird species that would be of interest to visitors. Hopefully this list as it grows will be of use to you in finding those species at the top of your wish list. Please note that at this time I'm not including a list of all the birds of California, just those that I feel will be more sought after.
Scott's Oriole-A bird of Joshua Tree forests and desert oasis/woodlands. I've personally found this bird in Joshua Tree National Park in the northern section of the park. Because of the heat during the summer months when the bird is present, it would be best to search for this bird very early.
Gray Jay-Coniferous forests of the northern portion of the state. Search locations like Lassen Volcanic National Park, the Mount Shasta area, and Van Damne State Park in Mendocino County.
Island Scrub Jay-Endemic to Santa Cruz Island off the coast of southern California.
White-tailed Ptarmigan-Mountains above treeline. From what I
understand this bird is currently restricted to the tundra above treeline in the area of Yosemite National Park.