Sept/Oct can be risky in the Caribbean due to hurricane season.... but it can be a great time, too. You just never know if a storm will blow thru. It can be rainy though.
The Fiji suggestion is nice, but diving there is drift diving and most dives are more advanced for that reason. You had said that you didn't want advanced.
If money is no object, as well as time traveling, I would think about Palau and Yap. The dives in Palau are drift diving also, but the boats pick you up when you surface, like in Cozumel. Many are considered advanced, due to the drift and the sharks.... but for me, it is worth the adventure. Sept-Oct is the rainy season there, but then it rains almost daily there year-round, it just rains a bit more during that timeframe.
As far as the WOW factor.... Palau is it. Every dive is a wow experience!
[vimeo]3506378[/vimeo]
sorry it is not HD, we were there in 2007.
Of course.... once you have been to Palau, no other place will be quite so exciting!
robin