Lindsay Books is a great source of esoteric books for geeks who are into physical sciences. The books typically have a homebrew focus, and you won't find these books at your big box book stores. As an added bonus Lindsay is moderately insane- so his advertising copy is good for a laugh.

Metal Working

Backyard Metal Casting is a great website run by Lionel Oliver. There are lot's of informative pictures and instructions. What he lacks in finesse he makes up for with enthusiam.

Budget Casting Supply is an online shop for the type of stuff you need for casting that you can't find at your local hardware store. Don't want to find old pistons to melt? BCS has aluminum ingots. Clay based greensand not behaving? BCS has premixed petrobond greensand. Shipping is included in the prices. Not cheap but very convenient.

Web Development

WebMonkey is a good how-to site for web developers. Have your html/css questions answered without getting up from your chair.