Here's a way to make a nifty vector circle thing. You'll need the align object plugin and BoltBait's flip plugins.
First, make a new layer and make a circle outline of the color you want the inside to be. Then use align object and make it in the middle.
Then, duplicate that layer and go to Hue/Saturation and turn the lightness all the way down to make it black. Make sure this black layer is on top. Now your canvas should just look like a black circle.
Make a new layer under everything, and make a filled circle to be inside the outline. Make sure the color is the color you chose at the beginning.
Go to your colored outline layer, and go to hue/saturation to make it lighter a little bit. Then, use the arrow keys to move it down, right, down, right, until it looks pretty good.
Erase everything that's outside the black outline.
Duplicate the crescent layer and flip it vertically and horizontally. Then adjust the lightness using hue/saturation and make it darker.
I think it looks pretty good. You can probably use it to emboss text and stuff too.