Who are the top selling female arrtists of all time?

Answer 1

I'd guess Madonna would be at the top of the list.

Answer 2

Mariah Carey was but not sure but she & Michael were the millennium winners in music:
Millennium Awards.
Apart from the world's best-selling artists in the various categories and the national best-selling artists, special millennium awards were presented in 2000, for the very first time to the world's best-selling recording-artist of all time [5]. The awards were presented to Michael Jackson and Mariah Carey in the male and female categories respectively.

http://en.wikipedia.org/wiki/List_of_Mariah_Carey_awards