Imagination and intuition are cousins, so if you want to spark your imagination, build your intuitive skills. I'm currently reading Divine Intuition: Your Guide to Creating a Life You Love, and it's proving to be the best manual on developing your imagination I've ever read.
The book's design is outstanding. Beautiful photos, mixed with inspiring quotes, and combined with author Lynn Robinson's deep understanding of what intuition is, how to develop your intuition, and why it all matters.
Here's a quote from the book. It's a Zen poem:
Sitting quietly,
Doing nothing,
Spring comes and grass grows
By itself.