Avocado.org
Last edited Sun Jun 3, 2012, 11:05 PM - Edit history (2)
We're growing an avocado tree.
Growing an Avocado Houseplant
Don't throw out that seed! You can grow a beautiful houseplant or even your own tree following these simple steps.
1. Wash the seed. Using three toothpick, suspend it broad end down over a water-filled glass to cover about an inch of the seed.
2. Put it in a warm place out of direct sunlight and replenish water as needed. You should see roots and stem sprout in about two to six weeks.
3. When the stem is six to seven inches long, cut it back to about three inches.
4. When the roots are thick and the stem has leafed out again, plant it in a rich humus soil in a 10-1/2" diameter pot, leaving the seed half exposed.
More: http://www.avocado.org/grow-your-own-tree/
For posterity, our avacado tree:
= new reply since forum marked as read
splitting apart. Thanks for this, a reminder to add some water. They need it 
We'll compare trees as they grow! 
should be fun 
I will post pictures of mine tomorrow ... too late tonight.
Never heard of cutting the stem back. Too late for this guy, but might try it with my next one! 
I know some plants with strong roots in water will re-grow leaves and I guess avocado must be one, but it still seems like undue stress on the growing plant. 
old glass spice jars on top of which the seed can rest without toothpicks (the bottom of the seed sits just below the lip of the jar and in water until the roots start). The toothpick method seems to result in some kind of rot or damage 3 out of 4 times I've tried it.