If things aren't ready yet for building a septic system or a blackwater-capable large scale Living Machine there are these quick off-the-shelf options.
Compact composting toilets;
(limited in capacity and so sometimes finicky. Compost suited to gardening, but people tend to prefer using it for non-food crops even if there's no technical reason for it. Must avoid chemicals and drugs in the blackwater stream)
Marine-type incinerating toilets;
(power hungry, expensive, uses consumable paper liners, needs good wind flow in the region and tall vent pipes, but the cleanest, most convenient, and low in maintenance -and helps keep the bathroom warm in winter... Ash is dry and odorless and can be safely put right in the ground or in the trash -or into the sea for that matter. Standard equipment on many yachts and for the Sea Room vacation housing developed by US Subs)
Larger scale composting systems;
Tends to need basement installations but serves whole buildings.
I also recommend this book, both for the art and the subject;
(from Eric Hunting)