1.
Start by creating a new image. For this tutorial I made a new 200x200 image with a white background. Next click on the create new layer tab to make a new layer above your white background layer. Next grab your rectangular marquee tool and make a selection similar to the one I have made ( make sure you are on your new layer and not the background layer ).



 

2.
Now click on your Linear Gradient Tool ( or press G on your keyboard to switch to that tool ). Click on the options tab and make sure you have a gradient like mine. You should have two black selectors, one on each end and one white selector in the middle. If you don't have a ready to go gradient like this one just click the new button, give it a name and create one.

3.
Once you have the proper gradient chosen it is time to fill the selection with that gradient. Start at the top of the selection and drag down to the bottom of the selection making sure you are dragging in a straight line.

4.
If the above steps were followed you should have something that looks like the picture on the left.


 5.
Now go to Edit/Transform/Skew and carefully take both the top point on the right and the bottom point on the right and drag them to the center. Now you should end up with your basic spike shape.

6.
As you can see we need to clean up the rough edges. To smooth out your spike go to Select/Modify/Contract and choose a setting of 2. Next go to Select/Feather and choose a setting of 1. Now hit Ctrl+Shift+I to invert your selection. With the selection inverted hit the delete key to clear out the jaggie pixels and then hit Ctrl+D to deselect the image. Now when we feathered it we lost a lot of detail so drag the layer with the spike on it to the create new layer tab to duplicate this layer. Do this 5 times. So you should have your white background layer and 6 spike layers. Now close the background layer by clicking on the eye next to it and then go to Layer/Merge Visible. Now you should be back to only 2 layers. The background and one spike layer.

7.
Now that we are back down to two layers drag the layer with the spike on it into the create new layer tab one more time. This will give us all our detail back but we have a nice smooth spike now. With the top layer ( the one you just made ) selected hit Ctrl+E to merge that one down with the original spike layer.

8.
Now give it a nice drop shadow if desired and play around with adding some inset areas and other stuff.... If you want to before you add the drop shadow and other stuff duplicate the spike layer and rotate them and add them to you graphics for some really neat effects...

Tutorial Source