Ask HN: how to monetize email list?

I'm fascinated by the story of Peter Shankman and Help-A-Reporter-Out making $1m / yr just from those little sponsorship paragraphs at the top of each email. Another interesting example is IdealBite.com, which sends out daily tips on eco-friendly living to several hundred thousand subscribers and sold for like $20m last year.

But what about the smaller end of the scale? Let's say you have a handful targeted email lists with 1000 - 5000 subscribers and you're sending out emails 1-5 times per week, with a typical open rate. What's the best way to monetize this? Is there a good provider of ads for something like this? Are there firms that you can outsource your ad sales to? Would love to hear any success or failure stories on this topic.