If you are a developer and confused with the look of your application, take a visit at iconspedia.com and you will get a bunch of icons for free. The icons are classified by many categories. I won’t write them here because it will take all page long. The icons are free and all of them are perfectly made.
Not forget to mention, there is IconBuffet where you can have different icon package each month and you must exchange your icons with other members to have all the icons sets available.