What can I substitute for sherry?

I use sweet vermouth if I am out of sherry.

My sister and I have found that flat Dr. Pepper used in place of dry Sherry gives an almost identical flavor to the finished dish. I know that sounds weird, but it works!

White vermouth is the accepted sub.

i was just faced with this problem in a soup recipe. i think it depends on the recipe but a lot of people said apple cider may work.... here are some other suggestions though
http://www.gourmetsleuth.com/Articles/Wine-and-Alcohol-644/alcohol-substitutes.aspx