I'm new to developing in Sharepoint, but not designing, so I thought I would throw a Photoshop tutorial out there for everyone. So let me take you through a few steps on creating a fresh icon for your Sarepoint site.
This is the icon we will be creating.
Step one create a new 250x250 canvas.
Then go to the Shape tool and select the Ellipse Tool. The color doesn't matter
Now add the shape to the canvas, after that is done double click the new shape layer and click the drop shadow option and set the distance to 0.

Now we are going to create a metallic feel to this shape so check the Gradient Option.
Right Click on Shape 1 and select Duplicate Layer.
Now double click the Shape 1 Copy to go to the blending options:
Uncheck the Gradient Option.
Check Color Overlay double click the Color Picker you can select a green or use this # 00ff0c
Check the Bevel and Emboss change size setting to 226, then click Ok.
Now it time to resize the shape so go to the Rectangular Marquee Tool highlight the Canvas right click and select Transform Selection. Adjust accordingly
Lets add a sharp refection to the top, the easiest way to do this is duplicate the last layer you edited and remove all but the color Blending Options, then change the color option to white. Click Ok
Right click Shape Layer copy 2 and Rasterize Layer.
Back on the tool bar click the Magic Wand Tool click in the center of the Shape now select the Marquee Tool and move the highlighted area to the lower right corner finally hit Delete. It should look like this.
On the Layer Options change the Opacity to 25%.
It is time to create a shape in the icon. Go to the Shape Tool, then select your Custom shape I went with the check shape. Also you can add a drop shadow like I did, or leave as it is.

And we are done! Now you can save and add it your Sharepoint intranet.