SENS is actively raising money. There is the issue that Calico might be pursuing several of the lines of inquiry SENS is with much more capital. But if this happens SENS will most likely pivot their active research.
The top of my list for organizations to investigate is currently the Brain Preservation Foundation. They administer the plastination prize. Robin Hanson outlines this a bit here. I think that contributing here is different from contributing to cryonics. Learning to preserve brain's structure moves multiple goal posts forward and has the potential to attract more research dollars into the area.
I've recently had the bad luck of having numerous people close to me die. Though I've wanted to contribute to anti-aging and anti-death research for a while, I'm only now in the position of being stable and materially well-off enough to throw around semi-serious cash.
Who should I donate to? I don't want to do anything with cryonics yet; I haven't given cryonics enough thought to be convinced it'd be worth the money. But I was considering the Methuselah foundation.
Suggestions?