If you're a newsletter fan (I think of them as email blogs), there are a handful of insightful ones about advertising and marketing to the 50+ demographic:
Matt Thornhill of The Boomer Project puts together a fun newsletter full of juicy, informative stories.
The Mature Market's newsletter has links to lots of original and reprinted articles from around the world. Find out how other countries are dealing with advertising and marketing to Baby Boomers.
Mary Furlong's newsletter comes out infrequently, but is always worth the wait.
One I don't subscribe to is Dick Stroud's newsletter. That's because his blog is an every day stop for me.
There are others - but they tend to be exclusively promotional newsletters touting the companies. (I call them opt-in spam.) Who needs a slightly different ad showing up in your mailbox every month?