BehindTheName.com is one site that offers a phonetic pronunciation guide for thousands of names. Other sites, including HowToPronounce.com and HearNames.com, offer audio recordings of many names as well.
BehindTheName.com provides information on how to pronounce a name depending on the language from which the name derives. For example, the page dedicated to "Olivia" lists its most common English pronunciation, as well as alternative pronunciations from the German and Finnish languages.
HowToPronounce.com and HearNames.com do not provide written pronunciations. Instead, these sites offer a list of audio recordings of names spoken by male and female voices of various backgrounds. HowToPronounce.com places the highest-rated pronunciations at the top of the list.