An all-in-one automagic, free and fast site where you upload an image and it generates "icons" for you. This *includes* a multi-resolution `favicon.ico`, but also icons for various other icon-using platforms, and it gives you little adjustable previews of each of those so you can get something that'll look right everywhere. For a favicon it's super-simple - upload, next, download, done.Real Favicon Generator
realfavicongenerator.net (archive)
If you need a little more hands-on control of your icon creation, this editor gives you a pixel editing GUI for each resolution that will be included in your icon. This lets you fix display errors from automatic scaling, and choose to exclude or include additional resolutions. It works for favicons, but it *shines* for PC icons, where it's almost certain that the beautiful 512x512 version of your graphic isn't going to look correct when *automatically* downscaled to 16x16.RedKetchup Icon Editor
redketchup.io/icon-editor (archive)