Here are some simple icon designs. I like how easy clean they are and each one has a specific opening to it that allows the icon to be a part of the background. I also like how they are all see through and tie in well the background also.:
10 vector badge templates for designing logos—free! - InVision Blog Thoughts on users, experience, and design from the folks at InVision.
Mathery Studio creates artwork for Wallpaper x Milk Magazine's cafè