I think Givewell is excellent if your goal is to donate to charities that have been vetted for maximum impact (measured in terms of cost-effectiveness of dollars donated to saving lives) but if you are looking for a charity in a specific sector outside of one they have judged, they're not the best for that. But if you're a founder by chance, founderspledge.com supports people in figuring out where to donate based on their interests (and also publishes some of their research).