Definitely SAN FRANCISCO and north. The "City" has it all: Painted ladies (Victorian houses), classical civic architecture, great museums where you can shoot paintings (without flash). In Golden Gate Park you'll find landscapes, water scenes, the Conservatory (Old Victorian bldg. with fantastic flora), The Japanese Tea Gardens, windmills, Lands end for ocean, cliffs, Golden Gate Bridge views. Just walking around neighborhoods (great mom & pop restaurants), Union square. The magnificent restaurant at the top of Neiman Marcus with the 50 foot oval leaded glass dome. The same at the Palace Hotel. Night time city scapes from Diamond Heights or Twin Peaks. Generally, the widest variety of photo opportunities you can think of. Take a ferry ride over to Sausalito and walk around and shoot the town and marina. Or drive North across the GG Bridge and travel up hwy. One and shoot the most beautiful coastline you've ever seen. Have lunch in Bodega Bay and turn inland and go toward Guerneville to shoot the redwoods and the wine country (you can do it as a day trip, but if you're on vacation, take two). If you want to keep going, you can go up to Sacramento and shoot the Delta, then on to Reno (great snow scenes in winter). The City is crammed with tourists in the summer, so fall might be best. Take warm clothes as San Francisco can be cold in the summer and fall. Check out the Corbis web web site (it's a photo service) and enter some of the things I've mentioned and see for yourself. Other than that, Seattle, Vancouver and Victoria in British Columbia.
Where ever you decide to go, have a great time and take extra batteries and large capacity memory cards.
Tom Beard