A lot of the knitting books that I consider really inspiring are ones that encourage you to go your own way, to embellish your knitting in some way or change a basic pattern or even just come up with a completely custom pattern for yourself.
Perhaps the queen of DIY knitting is Barbara G. Walker, whose treasuries of knitting patterns are classics, essential to any knitter who wants to get creative with her knitting. These books include thousands of knitting stitch patterns and charts that you can use for all sorts of knitting projects, from a simple washcloth to a sweater or skirt.
And if you don't know where to begin when it comes to knitting that sweater or skirt for yourself, then you also need Walker's book Knitting from the Top. This book explores the hows and whys of knitting different garments from the top down, beginning with a classic raglan pullover but also including hats, pants, skirts and capes (we'd probably call them ponchos today).
There's not a single by-the-numbers knitting pattern in this book, but the instructions inside could keep you going for a long time working different styles of garments in different stitch patterns from the top down, all perfectly fitted for your body. Sounds pretty good to me!