Anything by Julia Cameron gets me out of the dreaded block asap. I have quite a few of her books and I like her philosophy.
Another favorite is Natalie Goldberg’s Writing down the bones. If you like Buddhist / Zen writing, this book will be nice to read. Some of the chapters are not as interesting as the others (to me), but overall, I like her imagery, tips and habits.
Then there’s everybody’s favorite : Stephen King’s On Writing. I can’t stand King’s fiction. I began reading Carrie but wanted to throw up by the second page; haven’t touched another of his novels since. But I loved ‘On Writing’. I’ve read it a couple of times and each time I admire the man for his strength, courage and tenacity. That’s the kind of writer I wish I was.
Writing magazines give you inspiration by the bucket-loads too. I’ve just begun subscribing to Writing Magazine and get Writer’s News as a freebie, which is great because it is full of market information.