(This may be common knowledge, but I'm new at this mommy thing, so forgive me if it's old news).
If you need to renew your WPZ membership, Costco sells a standard adult membership for $30, and you can add kids for $8.25/each. You pay the normal price for any extra adults. The certificate does not have an expiration date on it. I think that's a pretty good deal when it's $17 for one adult to visit the zoo once!
Re: PSA: zoo membership deal
My Pregnancy blog
The standard membership (which is the Costco deal) allows you to get 2 half-price adults per visit, while the big expensive membership lets you get 5 per visit at half-price. Now I'm wondering if the zoo would let you use one of the Costco vouchers towards the purchase of an additional flex adult (for nannies, grandma, etc.).
*oh, and normally it's $11 to add children 3-18 to the membership