HIGH QUALITY BACKGROUND IMAGES
If you make your own graphics, most of these textures can be used as brushes in your photo manipulation software.
PHOTO MANIPULATION SOFTWARE / WEBSITES & FONTS
GIMP is 100% free and just as capable as Adobe Photoshop.
pixlr is also free, but web-based. There are 3 editors, but the advanced editor is also pretty close to Photoshop.
BannerSnack allows you to make flash banners. If you want an animated header, this is the place to go.
GIF EDITORS - add effects, resize, add text, remove frames, etc
FONTS - download and install on your own computer or use Google Fonts to embed directly into your blog
HTML / CSS / CODE RESOURCES
CSS explanations: http://www.w3schools.com/cssref/default.asp
Change your font: http://www.pagerank.net/css-font-style-wizard/
Change font, links, etc: http://www.somacon.com/p334.php
Resource site for CSS wizards: http://www.1stwebdesigner.com/css/powerful-css-tools-generators-automate-workflow/
Website Add-ons: http://www.entheosweb.com/website_design/free_web_tools.asp
Embeddable Forms: http://www.wufoo.com/
Translate your blog for foreign readers: https://translate.google.com/manager/website/
Social media buttons: http://www.niftybuttons.com
Everything and anything else you could possibly want to add or do to your blog: http://www.allblogtools.com/blogger-tools/
How to: Set up Google Analytics
How to: Use blockquotes
How to: Use "Shelve It!"
How to: Make reactive links
How to: Block people on BookLikes
How to: Batch edit your shelves
Lists of tutorials, tips, and the like:
I tried to link tutorials to the original poster. Please let me know if I failed on that.