I'm interested in making web graphics (banners, buttons, icons, backgrounds, etc.) Anybody know of a good book/resource that can help me get started? I'm fairly decent at Photoshop, and I'm pretty skilled with PHP (not like that will help).

If you know how to use Photoshop, it should be easy for you to create some basic graphics elements. I recommend you to just start artwork and play with them. Google for tutorials and learn about how to give different effects and image manipulations. Just start .. if you don't start you don't learn.

Honestly, I would spend your time completing tutorials which in my opinion will help you out a lot more than books. That is providing you have basic PS knowledge which you said you do. Try http://www.pixel2life.com , http://www.tutorialized.com , http://www.tutorialoutpost.com for some good tutorials.

One of my favorite website for graphics to visit is http://www.tutorialfx.com/forums/ But http://www.pixel2life.com and http://www.tutorialized.com are also great.

I would look at sitepoint.com's books and kits. I've bought three so far myself - usability, email marketing and web design business kit. I had the SEM one but as I'm an expert SEO I didn't learn that much. They generously accepted to take it back in exchange for the Usability Kit - after the date for returns had passed!! They probably have some great stuff on graphic design as well.