Since you are talking about prestige classes now, have you thought about Veiled illusionist from Paths of Prestige. The requirements are not too restrictive and you get some fun stuff, like illusion spells (Invisibility, image spells) from the wizard spell list.
If you are building a heavens oracle (or something similar), who will probably get Spell focus: Illusion anyway and doesn't have that many worthwhile revelations, veiled illusionist would probably be pretty good. It makes an oracle Illusionist a viable build.