CAMERA MANUFACTURER'S REMOTEThe most basic camera remote, if available from your camera's manufacturer, essentially will act as a wireless cable release, with the ability to fire the shutter or initiate and end a Bulb exposure (a long exposure during which the shutter remains open until you release it). More expensive models may include timer and intervalometer capabilities.
Though limited, these remotes are useful for group portraits, macro work and situations where it isn't practical or possible for you to be behind the camera. On the plus side, these remotes are relatively inexpensive and simple to use, and sometimes are even included with the camera. The future of these simple remotes is uncertain, though, with smartphone app control as a feature of more and more new camera models.
WIRELESS TRIGGERSIf your camera maker doesn't offer a remote for your model, there are options from PocketWizard, Phottix and others that offer trigger-release capability, some over considerable distances.
For more sophisticated control over your camera, with intervalometer and timer capabilities, Hähnel's Giga T Pro II wireless remote includes a self-timer, an intervalometer, long exposure and exposure counting. A repeat mode for interval shooting lets you automatically take a specified number of shots at a preset interval, then wait for a second preset interval, before repeating the program, as in "Take five shots, one minute apart, then wait 10 minutes, repeat." This is an excellent feature for time-lapse work.