IPS-LCD (in-plane-switching LCD) displays, found on the iPhone 4 and the Motorola Droid X (marketed as a "Retina Display"), offers improved viewing angles and lower battery consumption than TFT LCD displays. Relatively powerful phones often use them.
AMOLED (Active-matrix organic light-emitting diode) display technology is gaining popularity in high-end phones like the Google Nexus One and the HTC Droid Incredible. The displays are much easier to view in bright, natural sunlight than their LCD counterparts; however, some users have noted that AMOLED displays are prone to rendering oversaturated colors. Supposedly, AMOLED displays require less power and thus conserve a phone's battery life; but in real-life battery tests, they consume just as much energy as LCD displays.
Samsung's Galaxy S was the first smartphone to showcase the company's own Super AMOLED technology. Super AMOLED puts touch sensors on the display itself, as opposed to creating a separate layer, making it the thinnest display technology on the market. It is also much more responsive than other AMOLED displays.
Smartphone touchscreens allow the user to interact directly with the phone's interface and operating system. These days, two main types of touchscreens are used in smartphones: resistive and capacitive. Resistive touchscreens contain two layers of conductive material with a small gap between them. When your finger depresses a point on the screen, the two layers meet and form a circuit at that location. The information from that circuit then goes to the phone's processor.
Capacitive touchscreens often appear in higher-end smartphones like the HTC EVO 4G and the Motorola Droid. These screens usually consist of a layer of glass coated with a transparent conductor like indium tin oxide. The human body also conducts electricity, so when your finger touches the coating on the glass, it creates an interruption in the screen's electrostatic field. The phone's processor then detects the location of that interruption.