iaza - this is a free service that aims "to make the conversion and manipulation of digital images as easy as possible". the options are divided into 3 main categories (but uses 4 columns): Convert & Enhance, Edit and Create and within that. there are a myriad of sub-options which can searched using the browser's Ctrl+F function. what makes it cool is that each step of editing/manipulating can be saved by right-clicking on the image and just use the browser's back to undo any changes.
i just tried out a few images and things couldn't be easier. i used an image i found online, to crop, add a transparency layer, and finally convert into png. the results are quite impressive even though it's missing a "Convert To ICO" option. so, if you're in a hurry, you can give this online tool a spin.
iaza: Online Image Editor/Convertor•
http://www.iaza.com/