Re: agent
Well, I got about three years before I ended my subscription, and I kept a lot of the interviews (James Lee Burke, Tracey Kidder, Stephen King, Evan Hunter, etc), which were the best part of it. (I wasn't on the web then, where you can get any interview you'd like.)
It's a good place to start, with information on the business of novel proposals and such, and you can also find a lot of information on their website and newsletter.
Three collections of their material worth checking out:
Make Your Words Work, by Gary Provost
A great beginning primer from his WD articles
Telling Lies for Fun and Profit, by Lawrence Block
A collection of hard-earned words from his own column
The Writer's Digest Guide to Good Writing
A best-of collection of 75 years of their articles. My favorite part is 28 pages of quotes in the middle, including those from Louis L'amour, Allen Ginsberg, Isaac Isminov, John D. MacDonald, Henry Miller, and Tom Clancy. You can get it pretty cheap, and it's worth it just for that section.
Finally, you might want to check out their book club - there's some great selections there. 4 books for $12 plus shipping ($20).
Have a great Christmas.