I have two apps that I use - Dozzzer and Thunderspace.
Dozzzer will play your music at any given volume, and then slowly make it quieter, until the very end of your playlist. That way you can put on some music to sleep to, but won't wake up when it stops. There's an iPad version too for those who'd rather not wear headphones/earphones while sleeping.
Thunderspace is one of the newer ambient sounds apps I've been trying out. And I think it might be my last. It includes two sets of rainscapes to begin with, and they'll sell you the rest at $6.99 (for the moment). The cool thing is that it simulates lightning by flashing your iPhone's flashlight in time with it. Although I don't use that because it's just silly. Haha.
I usually fall asleep around 8/9PM though, so unless I wake up stupidly early (like 3AM), I don't use them.
I leave Reeder and e-mail for when I'm actually 100% awake. 😀