Doesn't even need to be free, just cheap!
We were using Groupspaces to host a small non-profit expat club discussion list. (ciwcro.com) They just reduced their free account from 250 members to 50 members on the discussion lists. We have about 70 members, with very little expected growth. We are looking for Mailman hosting with enough "bulk mail" allowance for the list to send maybe 1O emails to each the list a day usually it is only 2 or three. I would think 1000 emails a day would usually suffice.
We only want Mailman hosting for a subdomain, e.g. list.ciwcro.com. Our current web host is very restrictive on the number of emails allowed.