Go n-eiri leat (pronounced: Go niyree lat) = Irish for "Good Luck!"
Most commonly used in the phrase "Go n-eiri and bothar leat" (Go niyree an bow-har lat) meaning "May the road rise to meet you" (May your journey be safe and easy). This phrase is generally used when people are heading off on a trip. Of course the trip doesn't have to be all that long. It could be a trek to the other side of the world, or simply a short walk home from the pub!
"Go n-eiri leat" is used in much the same cicumstances as in English (exams, interviews, etc.).