Espresso and Cappuccino References

A good friend just bought an Expobar Office Control on my recommendation, and asked for some tips to get started. This is about the 4th friend I've directly influenced into getting a serious home espresso machine, so I figure it'll save everyone some time if I put in one place the better reference material I've found over the years. If you find anything else, feel free to leave it in the comments.

The basics:

Whole Latte Love does a great job of explaining the basics of how to make espresso. (They've been great over the years as a retailer of espresso machines; between my dad and I we've bought more than a handful from them.)

If you learn well by reading, these three articles should be all you need:

The Golden Rule - explains the key aspects of an espresso.
The Ritual of Making Espresso - step-by-step instruction on how to do it right.
The Art of Frothing Milk - hint: it's not about "froth" at all. A quote:

"I can tell you only that, once you’ve tasted [microfoamed milk], you’ll never again voluntarily settle for plain ol’ hot milk. Microfoamed milk is luxuriously textured but it is not what you would call thick. It pours slowly, more like a premium white interior latex paint and less like a yogurt shake. Call it oozy, soupy, or gloopy. Call it mucilaginous, if you absolutely must. What do you say we call it velvet chiffon?"

I'll add more in a bit...