I pronounce it like "TAL(rhymes with pal)-ee-uh". But I hear "TALL-ee-uh" just as often as I hear the way I would say it. I don't think there is a right pronunciation(not in the modern world anyways!) So, basically, I didn't help you at all...haha! :)
I also pronounce it like TAL-ee-ah.
I new a girl who pronounced it ta-LEE-a. Her family was from Mexico, so I assume it was a Spanish pronunciation. I'm not sure there is a "right way" to pronounce it, because, like you, I've heard it lots of different ways. I say pick the one you like best.
I've been trying to figure this out as well! I've looked everywhere and it seems like there isn't a definitive (or even a prominent) pronunciation. The name's so unique that I think you can just decide your favorite pronunciation and go with it. I've read a few sources that say the original Greek pronunciation is thuh-LIE-uh, but I don't hear that near as often as THAHL-ee-uh or TAHL-ee-uh. It's gorgeous whichever pronunciation you choose! :)
THAY-lee-uh for me.
If I saw this name, I would pronounce it TAHL-ee-uh. Very pretty!
Thalia is one of my favorite names. I'm Greek (but I live in the USA if that makes a difference, I'm not from Greece) and I met a girl a church named Thalia (I should've known I was a name-nerd because when I met her I said, 'OMG I love your name!'). She pronounced it THAL-ee-uh, and that's how I've always pronounced it and I prefer that pronunciation over the other ones. In Greek the name is Θάλεια, which would directly translate into Thal-ee-uh (I took 4 years of Greek language classes, so I know the alphabet and pronunciation pretty well, but don't hold me to it because its been a few years). I've heard people say that it should be Thal-LYE-uh in Greek, but I'm pretty sure that's wrong. I've heard other people pronounce it in many different ways, especially online. This would be one of the names that everyone pronounces their own way. I would say just pick the way that you like best and go with it.