This is not directly related to ASP.NET but might be very useful for general web development, check out these great free online tools from Dynamic Drive :
Use this online tool to easily create a favicon (favorites icon) for your site. A favicon is a small, 16x16 image that is shown inside the browser's location bar and bookmark menu when your site is called up. It is a good way to brand your site and increase it's prominence in your visitor's bookmark menu.
Email Riddler is an online tool that encrypts and transform your email address into a series of numbers when displaying it, making it virtually impossible for spam harvesters to crawl and add your email to their list.
Try Email Riddler
Gradient Image Maker
Gradient images are used everywhere in web page design, ie, as the background of form buttons, DIVs, to act as shadows and other interesting visual effects etc. We created this online tool to allow you to painlessly generate a gradient image of 3 types, with instant previewing so you get exactly what you had in mind.
Try Gradient Image
Image Optimizer lets you easily optimize your gifs, animated gifs, jpgs, and pngs, so they load as fast as possible on your site. Furthermore, you can easily convert from one image type to another.
Try Image Optimizer
Badge Button Maker
Use this online tool to easily and visually create those popular "XHTML valid" micro buttons (80x15). You can also opt for the larger 88x31 button instead. Enjoy!
Try Button Maker
I think later I'll post about others great free online resources I use a lot, buttons generators, xhtml templates and stuff like this.