I have been going to the San Diego Zoo at least six times a year for the past two years, and I am still not sick of it.  Having an annual pass that allows any guest and me entrance for free, makes for a cheap and easy last-minute outing with any friend or out of area visitor.  With free parking and free admission that leaves quite a bit of wiggle room for the food and beverage budget!  One of the best secrets is Albert's restaurant.  It is a full service restaurant with delicious food for a very reasonable price.  For just a bit more than what one would pay in the zoo's fast food court, you can get a full sit-down meal with great service and great ambiance.   There's a waterfall on the patio and also it is not uncommon to get a visit from one of the smaller zoo animals!  It's a little hard to find, but worth it once you do. Throughout the year there are extended zoo hours where you can view the animals at later hours when they are more active and entertaining.  Here's an example of one of the animals striking a pose this last weekend