The Wii Remote (also known as the Wiimote) is the main controller used for the Wii. The controller is able to accept connections from other peripherals, such as the Wii Nunchuk, Wii Motion Plus, Wii Pro Controller and Wii Classic Controller. An alternate version of the remote is also available, the Wii Remote Plus, that incorporates the Motion Plus functionality into a slightly longer controller.
The Wii Remote is shaped like a remote control, with a D-Pad and large A-button on the top. On the bottom (where the player's fingers would naturally rest) is a B button, that will act like a trigger button. At E3 2006 Nintendo showed these slight variations to the controller. The "b" and "a" buttons are now "1" and "2", respectively. "Start" and "Select" have changed to "+" and "-". One of the biggest changes, however, is the inclusion of an internal speaker in the microphone, allowing for "depth of sound", and presumably the "+" and "-" buttons will change the speaker's volume. The "home" button, probably for Wii menu accessing, also now looks like a house.
In addition to these features, the Wii controller also has a power button (like the Xbox jewel) built in rumble features (of course) and, most surprisingly, the ability to transmit it's exact location back to the Wii system. This feature functions like a 3-Dimensional mouse, allowing the game to respond to any and all movement of the controller. You can slash it like a sword to slash in a game, or swing it to simulate hitting a ball with a tennis racket, or twist it slightly to turn in a racing game. It is held with one hand.
For more traditional control, the controller can be turned 90 degrees so that players hold it sideways, turning it into an NES-like controller, which would have the 1 and 2 buttons function as the A and B buttons. This is to help play downloadable NES ports. There is also a "classic controller" that can be attached to the Wii remote, which features a shape like the SNES controller, but with two analog sticks at the bottom like the PlayStation's Dual Shock.