1. Methanogens: These are strict anaerobes that produce methane as a byproduct of their metabolism. They are commonly found in environments like swamps, the guts of animals, and even sewage treatment plants.

2. Halophiles: These archaea thrive in extremely salty environments, like salt lakes and salt flats. Some species can even tolerate salt concentrations as high as 30%.

3. Thermophiles: As their name suggests, these archaea love heat. They are often found in hot springs, hydrothermal vents, and other environments with temperatures above 80°C.