Chewing gum can help promote saliva production and, in turn, help with dry mouth. You'd want to avoid the types with sugar, though, since having a dry mouth can put you at a higher risk of tooth decay, as it is. At the same time, a lot of sugar substitutes, like aspartame, aren't good for you, either.
I chew gum sweetened with Xylitol, an all-natural sweetener that has actually been shown to prevent tooth decay. The brand I usually buy is called Spry, but there are others on the market, too. You can buy it at health food stores or order it online. (Usually pricing is better online, so I'd recommend going that route). Hope this helps.