So How Do You Pronounce “R'lyeh”, Anyway?

I subscribe to the apostrophe / boing methodology[0] so "reboinglyeh".

[0] http://issendai.livejournal.com/429293.html

I've always heard it in my head as Urrr LllYeh (sounds a bit like you are saying "oh yeah," except in a guttural voice, with your mouth full of blood)

/ˈɹu.li.a/ or /ɹɪl.ˈai.ɛ/