I hate the use the phrase "hidden gem", but Local Motors is one of the coolest places that I have never heard about in the valley. This is a small custom car factory that builds the Rally Fighter . I have seen the Rally Fighter vehicle in magazines and videos but to see them in person in various stages of completion was truly a treat.
Although I have never patronized Local Motors, I have to stop by their Yelp page with a 5 star review because I attended an incredibly fun event on February 9th, 2013. They held an open-house tour of the facility with free food, drink and autocross. Everyone there was a true gearhead and very friendly. Here is a short video of the auto-x festivities: http://www.youtube.com/watch?v=ZEuiiTId7dM
They post Rally Fighter videos and events on their Facebook so if you plan to visit, I recommend starting there. Very cool group of people!