Easy Bake Icon can make an icon with multiple sizes from any image that Image Events can handle: BMP, GIF, JPEG, JPEG2, MacPaint, PDF, Photoshop, PICT, PNG, PSD, QuickTime Image, SGI, Text, TGA, TIFF.
Easy Bake Icon uses tools built right into the Mac OS (Tiger tested only). After dragging image(s) onto the droplet, Image Events makes different sized tiff images from your original. Next it merges them together with the tiffutil unix command. Then it makes that tiff file into an icon with the tiff2icns Unix command. Finally, it cleans up the tiff files it created. You then choose whether to view or not to view the icon.