What child doesn't love to visit all the great animals at the zoo. My tip pertains specifically to the Memphis area though I know there are deals like this in other areas.
Current admission rates at the Memphis Zoo are $15 for adults (ages 12 and up) and $10 for children (ages 2-11). Parking is an additional $5. For our family, admission would run $75 for a one time visit! The problem with paying $75 to visit the zoo is that I then feel the need to see it all to get my money's worth. Trying to see everything in one day with littles is exhausting. The solution - purchase a family membership for $100. Parking is free for members and a bi-monthly magazine is also mailed out that keeps us up to date. There are also other discounts (a percentage off in the gift shop, discounted birthday parties, etc). For us the best part of the membership is that we can come back as often as we like so I don't feel like I have to see everything all at once.
And that is my tip. Search for family memberships to your favorite places to visit so the visits can be kept low key (ie short) and when there is a toddler melt down - go home and come back another day.
Be sure to visit Melissa at Coffee with Me for some other great tips (I'm loving the one I got from Beck about using our Klean Kanteens on a daily basis - What a great idea!!!!)