The Internet is replete with seemingly countless pages devoted to helping web designers/developers with their jobs. While many may in fact prove useful in this task, there are 5 that - in my mind - standout as truly being bookmark-worthy. In no particular order:
1. CSS Menu Maker:
An extremely useful site that allows users to create and customize their own CSS menu navigation. Options include both horizontal and vertical layout options, sub-menu navigation and more! http://cssmenumaker.com/
The W3C's markup validation page will check your site code for you and notify you of any errors and/or warnings that could prove problematic. A developer-must!
Another design-essential! View, create and customize your own color pallets with the Color Scheme Designer. See color compliments, triads, tetrads and more as you dial-in that perfect project color scheme. http://colorschemedesigner.com/
4. Grid Designer:
The Grid Designer is an invaluable resource for designers using a grid layout of any kind. The site allows users to enter the desired grid and typographic information, and then generates the appropriate column, gutter, and margin widths needed to complete the given grid layout. http://grid.mindplay.dk/
An impressive collection of Photoshop tutorials that are built for the novice and expert user, and nearly every level in-between. http://psd.tutsplus.com/