The RedKetchup - Icon Converter allows you to convert an image into a compatible Windows icon online. It can also customize the icon background with a color or adjust its rounded corners. Finally, it can configure the image format and the color depth used internally by ICO files.
Ordinatore - Those who want to tidy up their Macs will surely love this application.
png2ico - Program to convert .PNG files to a Windows icon resource, such as used for website/bookmark icon favicon.ico. Available for different platforms.
ConvertIcon! - Converticon is a simple icon utility.
Online Image Converter - Online Image Converter converts your BMP, JPG, PNG, GIF or ICO files quickly and easily.
GenFavicon - Generator Favicon.
ConvertICO.org - Create icons from png, jpg or bmp images easily.