There are precious few interesting gourmet food places in the West Valley, but Olive Gourmet is one of them. Located on Northern just west of the 101 in the Park West Mall. Sample both plain and flavored olive oils, and flavored balsamic vinegars. It did strike me as odd that you sample the oils and vinegars straight and not with bread or crackers, but I suppose you get a better sense of the flavor that way. Word to the wise- do NOT fill the entire sample cup with olive oil or you will feel obligated to drink it all! I find that just enough to cover the bottom of the cup is about right for a good taste.
The owners are in the store all the time and happy to help or chat. Surprisingly enough, the prices are pretty reasonable, even (or maybe especially) for the aged balsamic vinegars. They also have a stamp card where after purchasing a certain number of bottles you get one free.