Earlier today I was surfing web-related tutorials and came across this great tutorial on creating some killer N.C. Wyeth-looking clouds. I did this while I was on the phone with a client--about 20 minutes worth of work.
There are more awesome tutorials here. These tuts are geared more towards digital artists in the commercial art/motion picture/gaming industry--but the lessons are applicaple to ANY kind of illustration. Craig Mullins has a couple of great tutorials as do several other artists. I spent several minutes today just looking through them. I would invite you, gentle reader, to also browse through this wonderful site and engage in some "tutorial joy."