Christopher Knight from EmailUniverse has some nice tips for coming up with email newsletter ideas.
One problem he talks about is how you’ll always have good ideas and come across interesting articles, links, etc., when you’re not "in ezine production mode."
One thing I’ve been doing lately is keeping next month’s email newsletter in DRAFT mode in MailChimp. Then, as I come across ideas (or as I write blog posts), I go in and write a quick blurb in my email newsletter and save it for later. I’ll schedule it to send (to myself) about a week before it’s due to go out. Sort of a reminder to get it wrapped up.