VoiceOver has been significantly improved in Lion. In particular Apple has over 100 voices in dozens of languages. Voices that haven’t been installed are automatically downloaded when enabled.
The list of categories for the voices is below.
English (United States) – Female, English (United States) – Male, English (United States) – Novelty, Arabic (Saudi Arabia), Chinese (China), Chinese (Hong Kong SAR China), Chinese (Taiwan), Czech, Danish, Dutch (Belgium), Dutch (Netherlands), English (Australia), English (India), English (Ireland), English (Scottish Standard English), English (South Africa), English (United Kingdom), Finnish, French (Canada), French (France), German, Greek, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Norwegian Bokmål, Polish, Portuguese (Brazil), Portuguese (Portugal), Romanian, Russian, Slovak, Spanish (Mexico), Spanish (Spain), Swedish, Thai, Turkish