Sunnyvale got its wide variety of low cost rent places and decent Indian and Cheap and good Asian food places. El Camino Real is basically a mobius loop of America e.g. McDonalds, Starbucks, Ethnic Zone, repeat. Sister used to live in Mountain View off 85 by the Albertsons. Personally, if you're gonna live in Mountain View, somewhere close to downtown Castro Street would be cool to get food and beers and that kind of stuff. A bunch of startups (Meebo?) are around that area too.
Foster City is quiet. They have a bunch of golf courses and a Costco going for it. San Mateo is just about in the middle of everything, I like it because of the laid back downtown and being 5 min from the airport, 15 min from SV, 20 min (no traffic) from the city. That being said, San Mateo dies after 9pm. So if you're one of those party types lookin for a midnight saturnalia, the city is your only hope.