No doubt, fresh juice is a great idea for you (its healthy and alive!) and the environment (no plastic or glass bottles!). Nearly every member of the fruit and vegetable families can be shoved through a juicer to be turned, with great success, into easily downed, highly nutritious juice (just don't mess with bananas—they'll clog the machine).
But what of the leftovers, also known as "pulp," "stuff," and "juicing junk"? The residual fruit and vegetable matter that's spat out once the juice is extracted? 'Tis not junk at all! There's loads of nutrition left in that pulp, and here are a few ideas for making it useful (to things other than the compost bin).
There are tons of ideas on the Post Punk Kitchen message board. Some sound more appealing than others. What I could imagine doing: adding fruit or veggie pulp to muffin batter, using fruit pulp to make a sauce for crepes, and feeding it to guinea pigs.
Bloglander has lots of ideas too, like pulp-based pasta sauces and fruit desserts.