To save the most lives, select Against Malaria Foundation as your charity. It's the current top recommendation from Givewell (http://www.givewell.org), an excellent charity evaluation organization. They focus on proven cost-effectiveness and transparency.
AMF can save lives at a rate of $2500 or so per life saved, which vastly outperforms most other giving opportunities, at least if you require a high standard of evidence. Givewell's evaluation of AMF is here: http://www.givewell.org/international/top-charities/AMF
The second thing I thought was that I'd never remember to use it.
Just whipped up a tiny little chrome extension that will always redirect you to smile.amazon.com when you go to Amazon. It's not well tested, so could screw you up a bunch, but figured I'd share.
I wonder how Amazon plans to deal with the inevitable "why did you donate to a charity supporting / opposing $ISSUE?
Edit: well kids that's what happens if you comment before coffee - a negative take on something that has a decent potential to up the level of giving USA wide by a huge margin. Visit givewell.org and choose your favourite.
may as well make that prime account count - let me know when the UK can join in too.
We also have a lot of other merchants signed up.
A 0.5% effective rebate on everything you purchase on Amazon is better than many bank accounts offer...
http://www.businesswire.com/news/home/20131030005299/en/Amaz...
http://www.reddit.com/r/AdviceAnimals/comments/1pu5wh/a_simp...