To limit the candy intake in your own home, Simple Organic has some great ideas. They suggest you could try a visit from the Sugar Plum Fairy. You allow the child to pick out some favorite pieces of candy to have after trick-or-treating, then leave the rest out in a nice container or plate overnight for the Sugar Plum Fairy. The fairy takes it back to the fairy village and they use the candy to help build houses and homes. In exchange, the fairy leaves a new book, craft kit, new toothbrush, coloring book, or other gift of your choice. This way the child enjoys a limited amount of candy in moderation, but doesn't feel deprived of their bounty.
Another idea is to donate your candy. Doctor's offices, Libraries, and many other businesses often have a candy jar out for public consumption. They might appreciate the free donation of your left overs. Mom or Dad might have success taking the candy to work and leaving it out in common areas in a bowl or jar for co-workers to snack on throughout the day. I'm not sure on the policy of your local Homeless Shelter, but you could call them and ask if they would be interested in your candy donation for their residents.
Plus, being a military wife myself, I advocate Operation Shoebox. They welcome donated Halloween candy and distribute it to troops overseas. You can send a one-time donation, or sign up to Adopt-a-troop. Including a child-made card is always a nice way to say thank you.
Working with your child, set aside some candy that will be used for activities only (not consumption). Perhaps you use the wrappers for a craft project (but pitch the candy). Choose a variety of colors and shapes of candies and wrappers and use for a candy sorting activity. Some candy can be saved in a tin for making a Gingerbread House later. If you are feeling ambitious, Science 2.0 has the Top 10 Scientific Uses for Leftover Halloween Candy.
Candy isn't the only fun option at Halloween. Try handing out bundles of crayons or colored pencils tied together with a rubber band or ribbon. The dollar stores often have large bags of Halloween rings (spiders, pumpkins, etc.) that children love to receive. Bulk stores like Costco and Sam's Club will commonly sell large packages of mini cans of Play-Doh. Mini bottles of bubbles are also sold in bulk usually in the party favor aisle of many stores. Halloween stickers, temporary tattoos (buy a package and cut them up into individual tattoos for handing out), seasonal pencils, erasers, Halloween magnets (just make sure they aren't a choking hazard), packets of apple cider mix (like Hot Chocolate Mix), granola bars, and baggies filled with air-popped popcorn are also good alternatives. Juice boxes or small bottles of water are also a popular alternative, and trick-or-treaters will always be thirsty when they are walking around the neighborhood. Be aware that not all parents will allow their child to eat home-baked or homemade goods meant for consumption as a safety precaution. It might be best to stick with pre-packaged items to ease other parents' minds.
There are also Organic and Natural options for Halloween Treats: