Anyone know where I can get a comprehensive list, including the broad-based indexes and ETFS that qualify?
I'm assuming you're talking about option trading. AFAIK the underlying has to be a futures contract like ES, YM etc or an index such as OEX, SPX etc. I don't think you get 1256 treatment with ETFs. It's only indexes. The distinction is whether something cash settles or not. ETF options do not.
since IRS has no clues you are free to use form 1256. Also note: I am not a CPA. Disclaimer: I am not a lawyer. This communication is not intended as legal advice, and no attorney client relationship results. Please consult your own attorney for legal advice.
while it's true the IRS has no specific guidance re 1256 cars, i strongly suggest seeing a tax attorney and/or erring on the side of caution and either only claiming INDICES as 1256 for tax purposes or NOT claiming ETFs at 1256. see the below list. http://www.tradelogsoftware.com/support/user-guide/support-index-options.php