One of the nicest things that Mary and I received for Christmas last year was a family membership to the Cincinnati Zoo. (Again, thank you to my Uncle Dick and Aunt Judy for such a nice gift!) If you have kids and never taken them to a "good" zoo, please do so. There are several GREAT zoos in the world and not all of them are just animals sitting around looking like bumps on a log.
Having a zoo membership is great, we can go when we want to, get in, and stay as long as we feel my son will tolerate it and then leave. We feel no pressure to "see everything" or be forced to move at break neck speed to go do something else, because if we miss it on this trip, we'll just come back in a week or so and see it again. The other nice thing is that zoo membership gets you into "associated" zoos across the US, so if I'm traveling to San Francisco and for whatever reason I just wanted to hang out with lions, I could go and show my card and either get in for free or at a steep discount. Most zoos will also give you a discount on food and items purchsed in the zoo to members, plus the usual other stuff that zoos do for members like member's only nights, zoo formal parties, and so on. But let's keep it to stuff you'll actually do - discounts on food is nice - especially when it's $3 for a bottle of water and you only pay $2.50 (yes, I'm cheap, but that $0.50 is going to pay for some nice trinket for my son).
So go out and see zoos, they're fun, realitivly inexpensive, and a great way to spend a day.
Also - if you want to see some of the photos I took (only the good ones) look in the photo gallary, they're after the Washington DC photos. I've also put some animated .Gif's at the very end of the gallery with an ocelot jumping and a cheetah moving at top speed.