Largest Refracting (lens) Optical Telescope:
Yerkes Observatory - 1 M (40 inches) - Williams Bay, WI, US

Largest Refracting (mirror) Telescope:
Keck - 10 M (394 inches) - Mauna Kea, Hawaii, US

Largest Space Telescope:
Hubble Space Telescope - 2.4 M (94 inches) - Somewhere over Australia (at the time of this writeup; orbits the earth approx. once every 92 minutes)

Largest Single Radio Dish:
Arecibo Observatory - 305 M (1,000 feet) - Puerto Rico

Largest Radio Interferometer:
10 radio telescopes scattered between Hawaii and the Virgin Islands in a Very Long Baseline Array (VLBA) - Equivalent to a radio dish of 6,000 km (3,700 miles)