We came on a Tuesday for half price (May-August)...Can't beat that deal.
My only complaint is that the admission is a little steep (normally $20 for adults) and then once you're in the zoo it's extra for the train rides, carousel, camel rides, sting rays etc etc. Kind of disappointing they charge extra for a bunch of activities when the admission is that high. But it's a beautiful zoo and we may be back on the discounted Tuesdays!
Free parking. Don't forget suits for the kiddos - they have a few awesome splash areas! Also, bring a water bottle to fill up and your own lunch since the prices here are crazy!