Making A Biosphere

No we're not talking about that crappy Pauly Shore movie (that was called Biodome anyway), we're talking about small glass spheres that contain a completely self-sustained, sealed environment.  There's water, alge, little bugs, and all sorts of stuff that can live off itself for several years.

Biospheres have been available for quite some time but they're hella 'spensive.  Here is a page describing experiments in creating a homemade Biosphere.  It points to lots of resources to get you started, and pages where you can check out the commercial ones.