If you are a fan of minimalism modern UI style icon, then Nano icons 8×8 px is best. Todays special is a collection of Free Nano icons 8×8 px created with a great attention to detail.
Download royalty free icon file and use it as you wish to use it. The credit for this neat freebie goes to Dribbble.com.
If you want more icon, you can check the Free Icons.