This reminds me of omg-facts.com which I follow on Twitter and greatly enjoy (@OMGFacts). Seems they're reasonably successful with 1.6mil followers and various subcategory accounts (OMGFactsCelebs, OMGFactsSex, etc.) Their strategy seems to be occasional cross promotion and funnel readers to their site which is laden with advertisements. That's one option. (1)
(2) Charge subscription fees (perhaps $5/yr) for a premium version of the mailing list and treat the free one as a light upsell. Assuming you get 5% conversion, that's $750/yr or $62.50/mo. You'll need to figure out what kinds of extras you need to provide for your audience to consider it worth pulling out their credit card.
Alternatively could beg for donations, but I would rather donate by buying something from you.
(3) Find a cheaper way to send newsletters. Given Mailchimp's price points, seems the only way to go cheaper is to do it yourself. This is probably not worth it for you.
(4) webwright's point of doing Affiliates. No reason not to do this, very little effort and adds value to the newsletter.
(5) Merchandise. Perhaps compile a book of a year's worth of factoids and self-publish? Could do a paid ebook or printed on-demand via Amazon or Lulu.com. Could also do calendars (the one post-it per day kind, or the monthly flip ones). Once you have some solid merch, you could try and peddle to other resellers.
I like all of these, but not at the same time. I'd start with affiliates, then make a destination blog that mirrors the content but has a bit more engagement and some ads (also mirror on Twitter/Facebook, start building a brand), then do a premium newsletter/merchandise, then someday when you're a kingpin with millions of subscribers you can look into rolling your own mailing server.
P.S. I subscribed to your newsletter via acangiano's link. Looking forward to it. :)