"ree-ar-nah", totally Australian! lol love it! btw, I just saw your profile and you have the same name as my sister! Awesome :)
I'd say
Rhiannon - ree-a-non (a short 'a', like how Americans start to say 'and', how is that done phoenetically?)
Rhianna - ree-AH-nah
"Chan eil tuil air nach tig traoghadh"
"Maybe surrounded by
A million people I
Still feel all alone
I just wanna go home
Oh I miss you, you know"
- 'Home', Michael Buble