Watch out for little kids, they flock to it, and get into the way real quick. South of Los Altos, in Milpitas, is the Vans Skatepark at the Great Mall of the Bay Area. This is just the best. A great place to bust out, but watch out on weekends, where again, little kids rampaged though and into your way. I should shut up.
Gear is required at all times in the park.
Last, but not least, there is Greer Park in Palo Alto, northwest of Los Altos. A compilation of bowls, a lot of guys do some sick stuff. Way tight, and from what I see, not to many kiddies around. A good place if you are advanced in vert or bowls. Gear is required, but not a lot of guys use it.