If you want to retire rich, you have to prepare for it throughout your career. Exchange-traded funds can be a good investment vehicle to use to build up retirement wealth, because their low costs and broad diversification can open up a wide range of different types of investments from which you can choose. Many ETFs aim to provide strong growth, but some are particularly useful to those who are trying to accumulate savings for retirement. The three below are some of the best ETFs to serve that purpose.