Mary Beth Owens is an author as well as an illustrator. In the library I found an interesting book of hers all about carribou.
She works traditionally, I'm assuming watercolor but I couldn't find out for sure. What I love about these is the delicate paint and patterning around the letters, and also the light narrative. She does a great job of illustrating an alphabet while still making things both legible, having a narrative, and engaging at the same time. Her paintings are very beautiful. She doesn't focus on alphabet drawings, but does more traditionally narrative work as well.
You can find more info about her books here: http://www.jacketflap.com/mary-beth-owens/106475