Android Quran: The best Quran App for more you can read here.
MX Player: Movie Player which supports almost any format.
Calculator: Basic Calculator for quick maths. Have made us dependable on it no more calcluation in memories.
HootSuite: Social Messenger for Twitter, Facebook, LinkedIn etc
Maps: Google Maps to find places, route, traffic etc.
Photos: Basic Gallery App for Photos.
Calendar: Google calendar for your reminders and appointments.
Hangout: Default app for Hangout and now SMS too.
Keep: Notes app which will sync your notes with google in cloud. Search able and editable from PC too.
Aldiko Book Reader: My Book Reader supports almost all format.
Timely: Best UI for a Alarm Clock. For more read here.
Phone Book: For calling 😉 this was the primary use of the Phone long back ;).
Play Store: For adding more apps.
YouTube: For online videos
ES File Explorer: Best all rounder File Manager which also includes music player hence no need for a audio player.
QuickOffice: Office App for basic Excel, Word and PDF files.
Whatsapp: Most popular Messaging App without it you feel disconnected.
Gmail: For your email needs.
Chrome: For your browsing needs.
Camera: Basic Camera for taking quick photos.
I hope many of my regular apps are yours too. Do let me know you favorites app in comments below.