Icon Replacer is a portable utility for Vista and Windows 7 operating systems to quickly change software icons with in a jiffy. The tool lets you change the default icon with custom one. For instance, you can replace Firefox browser icon with your desired one.
Before using this tool you need to remember a few things. Make sure that the application is not running before changing its icon. And, also note that it can only use icons that are 24-bit depth or lower.
The tool creats a backup of the original file before replacing the icon so that you can revert to the default one without any problems.

HappyIcon turns large images and photos into perfectly proportioned icon, XP profile icons and cursors with a minimum of fuss. Just select a graphic in .bmp, .cam, gif, .j6i, .jng, .jpg, .pcd, .pcx, .pic, .png, .psd, sj1, .tga, or .tif format or else scan a photo.