Can anybody suggest to me some good applications that make use of UIAccelerometer Class and some references too ?
BubbleLevel is a sample app that's nice and simple, yet demonstrates the UIAccelerometer. First source of reference for the class is here.
progmr suggests that you're looking for ideas for applications that can make use of the UIAccelerometer. BubbleLevel already hints at one major use of the accelerometer - that of knowing the orientation of the device.
The other major use is (obviously) tracking the acceleration of the phone, allowing for the interpretation of gestures, for instance: not just shaking, but gestures like you might use when playing a Wii game. This doesn't necessarily lend itself directly to knowing the velocity of the phone! (Integrating the acceleration gives you velocity + some constant factor unknowable without calibration.)