I came across a service for push notifications, probably a bit late to the table but I have only just needed push notifications in my apps.
Being a web developer my original idea was to host the service on my hosting and then that way I would be able to send as many notifications as I wanted without having to worry about any extra costs etc.
This seemed to be more problematic than planned as I had to have ssl and specific ports opened and my hosting is a shared hosting which means that its a bit harder to get this all implemented.
I did some research and found a number of online services that offered push notification but the one that I went with was http://www.pushwoosh.com as they offered the best free package. You get unlimited notifications and up to 10 applications. Other services like http://www.parse.com.
Push Woosh was perfect for me as I just needed bog-standard notifications and it was also pretty easy to implement too.