I used PhotoShop for years before I learned this little trick. Thought others here might find it useful.
How many times have you tried to bring the palette size down on a gif, but seen banding in one area of the result that forces you to go to a bigger palette than you wanted?
Photoshop has an under-documented feature that lets you weight the Color Table toward the colors in any specific area of an image. Just select the problematic area and leave that selection active while you convert to index color.
The indexing algorithm then throws more emphasis to the colors in those pixels than it does to the rest of the image. Very often the banding goes away, allowing you to convert to a smaller palette and still look great.
Since I learned this, I've been able to amaze my friends and family (well, at least other web design geeks).
One side effect of this feature -- make sure that no selection is active when you index, unless you want to weight the color table. Many times I've had funky results because I forgot to undo a selection.