Of all the spices, probably the most ubiquitous is pepper. (Some might say it's salt, but I don't consider it a spice because it's a mineral, rather than a plant.) Green peppercorns, white peppercorns and black peppercorns come from the same plant - the Piper nigrum vine. The stage at which they are picked and how they are processed determines the colour.
The green peppercorn is the unripe fruit and it can be used fresh, dried or pickled. It is aromatic and hot, but not as strong as black or white peppercorns. Black peppercorns are also unripe, but the fruit has been processed, fermented and dried in a way that develops the flavour - making it more pungent than the green variety - and turns the exterior black and wrinkled. White peppercorns are made from the fully ripe fruit, which is processed and the exterior removed, leaving only the white core. White pepper is the strongest and hottest of the three, and a little goes a long way. It's used in pale sauces, where the dark specks from ground black pepper would be unsightly. The Piper nigrum vine can also yield red peppercorns (which should not to be mistaken for pink peppercorns - those come from a different plant), but these are very rare.
The pepper plant grows best in tropical climates, so can be found in places such as Vietnam, Thailand, Malaysia and other Southeast Asian countries, as well as parts of China.