This article from OregonLive offers a good introduction to the sport of randonneuring. It also includes a glossary of key terms. I appreciate that the article is written by someone who had just finished her first 200k brevet, which gives it a good beginner’s perspective.
Bicycle Quarterly has a great article on what makes a good randonneuring bike (pdf). What you’ll find there is not a description of a race bike, but a bike that is good for long days in the saddle. I’ve recently subscribed to Bicycle Quarterly and received the first issue last week. The publication is a lot different that other bike mags, but thus far I’m really enjoying the read. It’s got practical articles about bicycle weight and tire width. Lance Armstrong wouldn’t be riding the bikes in the pages of BQ, but then again, I’m not Lance.