I assume that GiveWell is the most popular of them. I mean, if you donate to MIRI, it is because you know about MIRI and because you specifically believe in their cause. But if you are just "hey, I have some money I want to donate, show me a list of effective charities", then GiveWell is that list.
(And I assume that GiveWell top charities receive orders of magnitude more money, but I haven't actually checked the numbers.)