Larry, for a jar that size, I think you'd be best off sticking with only a single small plant. A miniAV might remain small enough. You could also check into Utricularias, Pinguiculas, and Droseras -- all carnivorous plants. Some of them do stay quite small although their flower spikes would be too tall for your jar w/ the lid on. [Course you can always just snip flower spikes off.] Selaginella might also be an option though it will at some point outgrow that size jar.

: )

how about a pilea, or even better, a venus fly trap!

Larry,
I don't know if anyone has replied back to you about the fly trap. I find that those are hard to grow- I live in the high desert of OR so I can't keep the plant cool enough. I do know that they can get up to 6 inches and can become robust. I'm not exactly sure of the size of your container. You might try something else. A mini African violet as suggested above would be your best bet. Or perhaps a very very small creeper (Gesneriads - Streptocarpus) with a bonsai ornament center peice. Good luck!