Quick thought: I expect that the most effective donation would be to organizations funding independent researchers, notably the LTFF.

Note that I'm an independent researcher funded by the LTFF (and Beth Barnes), but even if you told me that the money would never go to me, I would still think that.

• Grants by organizations like that have a good track record for producing valuable research, as at least two people I think are among the most interesting thinkers on the topic (John S. Wentworth and Steve Byrnes) have gotten grants from sources like that (Steve is technically funded by Beth Barnes with money from the donor lottery), and others I'm really excited about (like Alex Turner) were helped by LTFF grants.
• Such grants allow researchers to both bootstrap their careers, and also explore less incentivized subjects related to alignment at the start of their career.
• They are cheaper than funding a hire for somewhere like MIRI, ARC or CHAI.

You may be interested in Lark's AI Alignment charity reviews. The only organization I would add is the Qualia Research Institute, which is my personal speculative pick for the highest impact organization, even though they don't do alignment research. (They're trying to develop a mathematical theory of consciousness and qualia.)

I agree that there are multiple types of basic research we might want to see, and maybe not all of them are getting done. I therefore actually put a somewhat decent effect size on traditional academic grants from places like FLI, even though most of its grants aren't useful, because it seems like a way to actually get engineers to work on problems we haven't thought of yet. This is the grant-disbursing process as an active ingredient, not just as filler. I am skeptical if this effect size is bigger on the margin than just increasing CHAI's funding, but presumably we want some amount of diversification.