Where to find songs for your Passover seder

Singing is traditionally a major part of the Passover seder, and it certainly makes for a more festive and participatory celebration. But what if your repertoire of Passover songs is lacking or you can't remember the lyrics or melodies even for classics like "Dayenu" or "Chad Gadya"? Or what if you have an urge to accompany the singing on guitar (or some other instrument) this year?

Whatever the situation, we can help. Here (and in no particular order) are the best online resources we could find. Are we missing something great? Leave a comment below and we'll consider your suggestions.

Zemirot...