The non-spicy answer is probably the LTFF, if you're happy deferring to the fund managers there. I don't know what your risk tolerance for wasting money is, but you can check whether they meet it by looking at their track record.
If you have a lot of time you might be able to find better ways to spend money than the LTFF can. (Like if you can find a good way to fund intelligence amplification as Tsvi said).
You probably shouldn't donate to alignment research. There's too much useless stuff with too good PR for you to tell what, if anything, is hopeworthy. If you know any young supergenius people who could dedicate their lifeforce to thinking about alignment FROM SCRATCH given some money, consider giving to them.
If there's some way to fund research that will lead to strong human intelligence amplification, you should do that. I can give some context for that, though not concrete recommendations.
I am excited about donations to all of the following, in no particular order:
Maybe it's somewhat in bad taste to propose a project I am involved in, but I think that Max Harm's and Seth Herd's ideas on Corrigibility / DWIMAC need support. Ideally, in my eyes, an org focused specifically on it.
See Corrigibility as Singular Target series for details.
This is going to be an unpopular answer, but you should invest it in a fund you personally control that is pretty much equally balanced between: Google, Microsoft, Tesla, Apple and Amazon.
This maximizes the leverage you will have at the critical moment (which is not now).
I think there is far too much focus on technical approaches, when what is needed is a more socio-political focus. Raising money, convincing deep pockets of risks to leverage smaller sums, buying politicians, influencers and perhaps other groups that can be coopted and convinced of existential risk to put a halt to Ai dev.
It amazes me that there are huge, well financed and well coordinated campaigns for climate, social and environmental concerns, trivial issues next to AI risk, and yet AI risk remains strictly academic/fringe. What is on paper a very smart community embedded in perhaps the richest metropolitan area the world has ever seen, has not been able to create the political movement needed to slow things up. I think precisely because they pitching to the wrong crowd.
Dumb it down. Identify large easily influenceable demographics with a strong tendency to anxiety that can be most readily converted - most obviously teenagers, particularly girls and focus on convincing them of the dangers, perhaps also teachers as a community - with their huge influence. But maybe also the elederly - the other stalwart group we see so heavily involved in environmental causes. It would have orders of magnitude more impact than current cerebral elite focus, and history is replete with revolutions borne out of targeting conversion of teenagers to drive them.
Maybe there's a way to hedge against P(doom) by investing in human prosperity and proliferation while discouraging large leaps in tech. Maybe your money should go towards encouraging or financing low tech high fertility communities?
I just want to make sure that when I donate money to AI alignment stuff it's actually going to be used economically