Antennae

• Goonhilly Earth Station, the geek's answer to the Eden Project. Cornwall = FUTURE. 25 communications dishes (the biggest 32 metres across), 36 other dishes, plus transatlantic fibre (which doesn't count). Lat 50.048 lon -5.1761.
• Cutler VLF station, the US navy's biggest VLF transmitter, built in 1961 and pumping out two megawatts at 14-60 kHz, by which means it can transmit at 50 baud to submerged submarines anywhere in the north Atlantic sort of region. 26 towers, each 250-300 metres tall, with over 2000 miles of antenna cabling strung between and beneath them. Lat 44.6472, lon -67.2817; see also an eyeball.
• The High-frequency Active Auroral Research Program (HAARP), blasting (when it's finished) 3.6 megawatts at 2.8-10 MHz through a farm of 180 crossed dipole antennas right into the upper atmosphere. Its stated purpose is research on upper-atmosphere physics (it's an 'ionospheric heater', although it doesn't heat it very much - more of a warmer), but everyone knows it's some sort of weather control / plasma superweapon / star wars / mind control no-goodery. Lat 62.39167, lon 145.1467. See also the Russian answer, Sura (lat 56.10, lon 46.10) and the plucky European heater, EISCAT Tromso (lat 69.5864, lon 19.2272).
• I always thought the antenna farm at Rugby Radio Station (note there's a second page to that link) was rather impressive when my dad drove us past it on the way to north Wales. It had twelve 250 metre towers, and handled Britain's VLF signalling, but they've mostly been demolished (shame!). These days, it transmits the MSF signal, the UK's national time standard. Lat 52.3676, lon -1.1892.
• Arecibo. Nuff said. 305 metres! Lat 18.3435, lon -66.753083.
• DX 138 (antenna details in English), Europe's largest ham radio antenna park. 24 directional Beverage antennas, totalling over 2.8 km in length (and rather more in the winter - not sure how that works), plus a few other bits and bobs. Built by dedicated German ham Wilhelm Herbst to enable hams to pick up extremely remote stations (Brazil, Alaska, etc). I'm not sure exactly where it is - apparently, "12 kms from Jammerbugten/Skagerrak in Denmark".
• RATAN-600, the world's biggest radiotelescope, in Russia. Lat 43.831319, lon 41.592083.
• The Giant Metrewave Radio Telescope, the world's biggest radiotelescope farm, near Pune. Lat 19.096667, lon 74.05.
• BT London Teleport, BT's main satellite uplink centre in London, out in Docklands, on the site of a former telegraph works (whatever that is). Apparently, the site was chosen to guarantee that the view south towards the geosynchronous satellites it uses would not be blocked by future tall buildings, since you can't put such things in a river - cunning! Apparently, London is the teleport capital of the world, with six of the things, of which this was the first, opened in 1984. No idea how many actual dishes they have, but apparently there are 58 'satellite accesses' there, more than at any other BT site, including Goonhilly. Lat 51.499373, lon 0.058751.

Special bonus! Mobile antenna - the US navy's Sea-Based X-band radar (SBX), with a 25-metre dish - eyeballed!

Son of bonus! The Transmission Gallery - photos of the UK's TV transmitters.