One little known feature of Keynote is the ability to double shadow your text. This is great for either faking an emboss, or for really beefing up the shadow behind text.
The trick here is that text itself is treated as separate from the text box. If you select the text box, and apply a shadow, it’s applied to all text inside the box. But if you double click the box to enter into the edit mode, and select the text itself, you can also apply a shadow to the text. Apply both and you get a very thick, dark shadow.
For more advanced looks, you can totally change the shadow settings on each one. One example is to make one shadow black and down to the right, and another shadow white and up to the left. This gives you a fake emboss look. This effects really works well on backgrounds that aren’t pure white or black as the shadows show up better.
You could also set both shadows to a zero offset and make them different colors. We tried one red one with a blur of 3 and a white one with a blur of 20. This gave us a nice white halo with a slight red tint closer in to the text.