GJ 436 System (10.2 pc) - The second known red dwarf planetary system. Contains one of the first Neptunians discovered. Planet b temporarily later found to be the smallest exoplanet (about Uranus' diameter, though over 50% its mass) known to transit its host star and is currently the nearest (33 ly). Its temperature (712K) was measured to be higher than what it would be purely from radiation (520K), perhaps due to a greenhouse effect, somewhat higher than Venus. It was originally thought to have a layer of "hot ice", water solidified due to high pressures. It turned out that it was larger than thought and hot ice was not needed. It could still be a rocky super-Earth. It was later found to have a remarkably low levels of Methane and high levels of Carbon Monoxide for its 800K temperature. Possible explanations include Methane being changed into hydrocarbon polymers due to its star's ultraviolet radiation, CO being drafted upwards with winds, or observational defects. It's significant eccentricity suggests a possible neighboring planet. Planet c was announced to be the smallest known exoplanet (1.5 Earth's diameter), but was later retracted because variations in transit timing of the first planet did not occur and the proposed orbit would be unstable. It is still thought that a second planet of some kind is possible in the system.
HD 189733 System (19.3 pc) - Planet b (the first nearby Very Hot Jupiter, originally thought to be inflated) is the nearest planet discovered using the transit technique (62.9 ly). This is the first exoplanet to have its temperature mapped and was nicknamed Bull's Eye for its hot spot that is significantly offset from the starward pole. It is also the first exoplanet for which scattered light in the upper atmosphere has been detected and the second exoplanet with water detected and first with Methane and then Carbon Dioxide detected. It later was the first exoplanet whose gasses were detected from Earth-based telescopes. It was also found to spin up its star and magnetically interact with it, causing stellar storms. Hubble found that its atmosphere was a uniform blue haze.
HD 209458 System (47 pc) - Has first discovered transiting planet which was nicknamed Osiris due to the comet-like tail detected and the first exoplanet around a normal star to have its mass directly measured. The planet may be losing its outer atmosphere, or magnetism may prevent the ions from escaping. They detected water in its atmosphere (they had failed earlier), the first time this has been done for any exoplanet. 2nd Exoplanet with detected organic compounds; like HD 189733b, it has water and carbon dioxide, but it has a lot more Methane. Tracking carbon molecules with dopplar spectrometry caused it to be the first exoplanet detected to have winds, which are raging at 5,000 to 10,000 km/h. This is believed to cause hotspots to appear at terminators rather than at the star-ward facing point.
HD 80606 System (58.4 pc) - Multiple star system with a planet, which has a higher period (111 days) than any other known transiting planet and highest eccentricty (Halley's comet-like). Discovered in 2001, but found to transit in 2009. Its orbit brings it from epistellar distances to Earth-like distances. Planet is the first one for which changes in weather have been observed. Potassium was detected from the high wind regions of the exosphere. In 2010 it was found to be only one of the two out of all 79 known transiting exoplanetary systems that could not support a habitable Earth-like planet, since its elongated orbit would destabilize any such planets.
1RXS1609 System (145 pc) - Contains first exoplanet (full name 1RXS J160929.1-210524) imaged around a sun-like star, photographed in 2008 and confirmed to orbit star in 2010. The planet's very large distance from the star 330 AU causes problems for planetary formation theories. Some liken it to an unbalanced binary star system where one component gobbled up the vast majority of the dust. It has about 8 times Jupiter's mass and 11 times Neptune's distance. It could be a new type of sub-stellar object between a planet and a Brown Dwarf. First exoplanet to have its spectrum taken, which revealed evidence of water, carbon monoxide, and hydrogen. Its star is young enough (5 MY) so that the planet has not had enough time to cool (1,500 C) and thus detectable.
XO-2 System (149 pc) - Contains a transiting planet. The planet is a little more than half Jupiter's mass, but is inflated to just above its radius. It was the first planet found to have Potassium detected, which is an element long thought to a dominant source for opacity in hot Jupiters.
WASP-12 System (427 pc) - The shortest period transiting Hot Jupiter known and the first carbon-rich planet ever found (more Carbon than Oxygen). One of the two largest known planets at 1.79 Jupiter radii. Hottest known exoplanet at time of its discovery. Planet is being ripped apart by star. It is stretched in the shape of a rugby ball and leaves a ring around its star. Huge cloud of material detected around the planet containing elements never before detected on an exoplanet. It has much more methane than water vapor. It may produce shock waves as it plows through its star's stellar wind (the first evidence of shocks around an exoplanet, like Earth and Saturn's bowshocks), possibly produced by a strong planetary magnetic field. This could protect its atmosphere from being stripped away. It could have a diamond core and other terrestrial planets in system would have black spots on them and also be carbon based.
WASP-17 System (?) - An F6 type star which has the first exoplanet discovered in a retrograde orbit. Also the largest known exoplanet at 1.74 RJ and 0.5 JM. Discovered by transit. It may be "flipping" its star's axis. Orbit hints at a near planetary collision in its early years. One of the 6 out of 27 planets analyzed by the WASP team found to orbit backwards around its star in 2010. It was found to be abundant in CO, depleted in water and methane. It lacks a prominent stratosphere and has efficient day-night energy circulation.