I know I'm late to this party (CRAFT reviewed this a year ago!) but I just bought Digital Textile Design:

On first pass through (very briefly!) it looks fantastic. Just the right blend of inspirational and "how-to-do-it-ness." 

Digital textile printing is my "someday" hobby — sewing is very rewarding, of course, but I've gotten into a bit of a rut where I make the same things (cough, Heidi, cough) over and over again, because at the end of the day what I really want is a wearable garment. Right now the limiting factor for me is fabric — can I find fabric I love? That's where textile printing comes in — it holds the promise of being able to get ANYTHING I want, fabric-wise … but with a steep learning curve. 

So as a kind of down-payment on that someday-when-I-have-time-to-design-fabric, I've been amassing some books, including this one. Anything else I should be investing in? (I already have a [very old] copy of Photoshop and Illustrator.)