Better Beveled Text
In the Script-Fu menu, there is an option to add a bevel, but I've found it to be lacking, so I found a better way to create a bevel which I'm sharing with you here.
For this tutorial, I'll be using a 400x400 pixel image at 72 dpi.
Okay, first you're going to need some text, so go ahead and select your font and color settings and put some letters on the canvas.
Next, duplicate the text layer. Right click the new text layer, and select "Alpha to Selection". Then fill the selection with white. This will make your text invisible. Don't worry, it's still there. It's just white.
Press Ctrl+Shift+A to deselect all. Now with the white text layer still selected, click Filter>Blur>Gaussian Blur.
You should now be able to see the edges of your color text peeking through the blurred area of the white layer.
Select the original text layer (the one with color.) Go to Filter>Map>Bump Map. Make sure the blurred white text layer is selected in the first drop-down menu labeled "Bump Map" and that the map type is "Linear". You can get different effects with the other settings, so I encourage experimentation here. The only settings I changed in the rest of the options were elevation and depth. Everything else is default. Click Ok and watch the blue bar go across the bottom.
Once that's done, you are basically finished except the blurred white layer is still in the way. You can just hide it to make it go away, or if you wanted to, you could send it back behind the color layer, invert the color and use it as a drop shadow.
(click to embiggen)
Update: Ryan shows us how it's done in Inkscape.