25143 Itokawa1 is a near-Earth asteroid. It was discovered on 26 September, 1998 by the Lincoln Laboratory Near-Earth Asteroid Research Team at Socorro, New Mexico. It is classified as a potentially hazardous asteroid, as its orbit brings it to within 0.05 AU of Earth 2-4 times each century2.
Itokawa's primary point of interest is that it was the first asteroid that we both visited and returned from. In 2003 the Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa spacecraft, and in 2005 it arrived at Itokawa, landed, took a sample of asteroid dust, and then returned to Earth.
Although Hayabusa did not collect as many samples as was hoped, it did gather a lot of useful information. Itokawa is an irregular shape which is often described as a sweet potato shape; the Hayabusa science team described it as otter shaped. While it is not as drastically lobed as 67P/Churyumov-Gerasimenko, it has one large lumpy-potato ovaloid, and a second, smaller lumpy-potato ovaloid curving off at one end (the 'body' and 'head' of the otter, respectively). These are believed to be two separate bodies that gravitated towards each other and stuck together.
It also appears that the overall composition of Itokawa is that of a 'rubble pile', a mass of debris formed after the destruction of a larger body3. This is supported by the identification of particles that could only have formed by cooling within a more massive body. Analysis of the dust collected also confirmed that Itokawa is composed of much the same material as is found in most Earth meteors, chondrite. This suggests that near-Earth asteroids may indeed be the source of most of the meteors that hit Earth.
As solar system objects go, Itokawa is fairly well mapped, and has ten named craters and seven named regions (link). Although Itokawa will be approaching us again in 2036, no further missions are currently in the works.
1. Originally named 1998 SF36; the Institute of Space and Astronautical Science requested that it be named after Japanese rocket scientist Dr. Hideo Itokawa specifically because it was being considered as a target of the Hayabusa mission.
2. To put this in context, its nearest approach listed on the NASA website was in 1905, when it passed within 0.01156 AU, which is to say, 4.5 times further out than the moon.
3. We don't really have any information on this event, aside from evidence that the original body was at least 20 km in diameter, whereas Itokawa's longest dimension is only 0.5 km. (Source.)