As an on-again off-again vipassana practitioner (I managed to maintain a regular practice while I was living in Boston, but that was largely due to the fact that the CIMC [1] was on my walk to/from work), I would love to get involved in a rationalist meditation group. In my experience it is much easier for me to maintain a regular practice with a group, but simultaneously difficult to become a real member of that group as most tend to approach meditation as a religious ritual rather than a worthwhile practice in its own right with practical value. Having a group of people to not only meditate with, but actually have productive conversation about the experience of meditating with would be phenomenal.

1 http://cimc.info/