Innate ideas

In the early modern period, one of the central philosophical debates was between defenders of innate ideas (rationalists) and their opponents (empiricists). What are innate ideas? Why do rationalists think there are innate ideas? What are some common examples of innate ideas cited by rationalists?
How does Locke argue against the existence of innate ideas? How might a rationalist counter Locke’s argument? Which approach to human knowledge—rationalism or empiricism—seems more plausible to you? Explain your answers.