I start with my favourite two. I use them daily.
Reddit is fun (Android): Reddit for your smartphone. Works great, fast and has every feature I want. Awesome!
MyENIGMA (iOS, Blackberry, Android): It's basically WhatsApp but they encode your messages. Every 3 days they use a new code. As a result not even their employees can read your messages. Of course the NSA and your government also can't read it. Their HQ is in Switzerland. http://www.myenigma.com/en.html