The simplest, and most inexpensive compost bins I have ever had, turned out to be the best.
I simply took 7 wood pallets, (try to get the same size, if possible), and I placed two at the back, another in the centre of these two, to make two seperate bins. I used some treated posts to hold them in place in four corners, and nailed a few wood strips to bind them all togeather. I then placed two more at the front, and hinged them, so I could open the bins up when I wanted to remove the compost. I used wire to hold them closed.
Pallets offer air circulation, because of thier construction, are reasonably strong, and usually you can get them free.
If they rot in a few years, I'll simply pick up some more, and burn the old ones.
I turn the hose on them from time to time in the summer to keep the piles moist. One bin is for the current addings, leaves, lawn clippings, veggie trimmings that the hens don't like, etc.. The other bin when full is left to work, and dug out once a year. When empty that bid then becomes the "new' bin, and the other is left to compost.
Sorry I don't have any pictures, but I hope you can glimpse the construction method, I described. If you need further help, just PM me.
One of the best sites ever, for gardening in general, also offers this topic section on composting. Check it out.
http://www.theeasygarden.com/forum/viewforum.php?id=36