For a quick remedy, though most of the other suggestions I see here are good, the best I've found is ginger. Fastest is a piece of ginger candy or fresh ginger *under* the tongue. Ginger tea is good too.
A great one that you can get almost anywhere is a pinch of salt on the tongue.
And I agree with what others have written: If you are experiencing nausea a lot, then paying attention to your dietary choices and maybe seeking out a health professional can be important. The cause behind the nausea can sometimes lead to worse things.