good points all.
one thing important to notice about good sunset photographs is how often a water surface (lake, ocean, running water of some sort) is used as the foreground. this is because the best sunset colors come most often after the sun has set, rendering most foregrounds bland, devoid of light and detail.
yes, PS can bring up shadow detail extremely well but often you're left with an aesthetic imbalance; that is, the sky and sunset clouds and colors are so much more beautiful than the lightless foreground.
thus many photographers make great use of reflective water surfaces to mirror the light show in the sky and bring light, color and aesthetic balance to the foreground.
so what to do when you're landlocked without those wonderful mirroring surfaces?
well, choose your foregrounds carefully for strength & color (for example, the grand canyon or any other briliantly colored sandstone), silouetted shapes (think monument valley). light colored surfaces (like sand dunes) work well.
exagerating the foreground and lessening the amount of sunset sky will also work to balance the photograph. a really brilliantly colored sunset sky can go a long way with very little. a huge sky can be a wonder to behold but in a photograph often that wonder is lost if the sky predominates and creates the aesthetic imbalance of a boring foreground.
also, never forget one of the most important elements in landscape photography: the 180 degree rule!! look the other way, especially in the waning minutes before the sun actually sets. your foregrounds will be softly muted in magic hour light, side and front lit. and quite often clouds will pick up early sunset coloring. as well, the contrast is far more easily managed.
