"Push" for Sparrow for iPhone
Sparrow is my favorite e-mail client for my Mac and for my iPhone. The lack of push updates for the iPhone version is a minor annoyance compared to how great the app is, but it is still something that needs to come quickly. I came up with a "workaround" to get a notification when my email's come to me, but still no badge on Sparrow's app icon.
Basically, I set up the default Mail client again on my iPhone. Made sure push notifications were active, and then I moved the app too my junk folder on the last page of my home screens. Basically this hides the Mail app, you still get a push notification when you receive an email, and you can open Sparrow whenever you here the tone or the vibration of your phone!
It works for me. It may not be enough for you, but in the meantime it might be a solution for some.