I love hand-illustrations. The human element in them is so prevalent and accessible. It's like being given a personal invitation to take a peek into someone else's muse. Or sitting on someone's porch and quietly watching the sunset together, enjoying the audible silence and relishing the visual "WOO-HOO!"
Three illustrators come to mind:
Mattias Adolfsson. Yes, yet another great thing from Sweden! His imagination is so wide! His blog is worth perusing through several pages of his whimsical, futuristic Moleskein illustrations.
Keri Smith. Collage-extraordinaries! Her colors and textures are incredible. I always wonder what it would be like to watch her at work, how she gathers her materials and ideas. She's also written up some fantastic articles on creativity and I highly recommend her 100 List.
Craig Garrison. While Craig specializes in the digital realm (and all of his work is fantastic), I particularly enjoy his sketches.