Newsblur (a web-based RSS reader) added a newsletter feature a while back that's pretty useful if you want to mix RSS & newsletters in the same place. Set up an email rule to automatically forward your newsletters to a custom address and Newsblur will show them as if they're another site you've subscribed to via RSS.

I'm not a big fan of newsletters myself, but it's nice to be able to include those few sites that only offer newsletters in my regular news reading workflow.