Data Usage is one of the best apps that can help to mange data usage.
Internet Speed Meter Lite displays your internet speed in status bar and shows the amount of data used in notification pane. This helps you to monitor network connection anytime while using your device.
The app is completely Free.

FEATURES
* Notification display mobile and WiFi data on notification.
* Data tracker display daily data of each app when you open it.
* Data warning show warning if the data usage over limit number you set.
* App data usage display data for apps for a period of time.

PERMISSION
* Data Usage monitor your WiFi data usage.
* Read Phone State monitor your mobile data usage.

Pro Features
Notification Dialog
A notification dialog appears when you tap the notification having
- Graph to monitor last minute internet activity
- Time and usage of current session
- Today's app usage for mobile and WiFi
Smarter notifications
Notification appears only when you are connected to internet.
Themes support
You can manually select the color of user interface.
Blue status bar icon
Option to choose between blue or white status bar icon. (only for Kit Kat and below versions of Android)
Upload and Download Speed
Option to show upload and download speed in separate notifications.