I can't even remember the amount of times I've been asked to do a tutorial on this effect. You could create those Rap type diamond effects using the noise filter, however this technique creates a more interesting result. This is the original Tutorial on this effect, there have been several Rips of it in other places.

Step1:
Begin with the text you want to turn into the gold and Diamond "Iced Out" effect.
Right click on the layer palette and choose Rasterize layer.

This will make the text editable

Step2:
Make a selection around the text (Hold down Ctrl/CMD and click on the layer thumbnail)

Press "D" to reset to default colors

Filter>render>clouds

If the render menu is not available make sure you are in RGB mode.

Step3:
Now this is where we create the diamond effect.

Filter>Distort>glass

Choose the tiny lens texture and scale it down.

Use the settings as shown here.

Click OK to apply

Step4:
We now have the diamond covered look to the text. Its common to have a golden border with this effect.

Step5:
Apply a layer style to the layer, choose stroke.

The important things here are:

Position = Center
Fill type: Gradient, choose the default copper setting
Make the size 10

Step6:
Click on the Bevel and emboss option

Choose "Stroke Emboss" this will apply the bevel to the stroke we just made.

Crank the Depth up and set the size for the same as the stroke:10

Change the gloss contour until you get something that looks nice and metallic.

Click OK

Step7:
Here we have our basic effect. We just need to adjust the color to make it look more like gold.

Step8:
Apply a Hue/Saturation adjustment layer and push the saturation all the way up to 100

Tweak the hue until you get a nice gold color.

Step9:
Last thing we need to do is add some sparkles.

Load the assorted brush set that comes with Photoshop. (Click the arrow at the top of the brushes palette and choose load brush on vs. 6 :: On Vs 7 just choose assorted from the menu. When prompted select "append")

Choose the small starburst.
Make white our foreground color

Step10:

Tutorial Source