The vast majority of these have been around the moon. Here's a list of what I can find (Using Wikipedia):
- Luna- 2 (Spacecraft and rocket)
- Ranger- 4, 6, 7, 8, 9
- Apollo LEMs- Apollo 12, 14, 15, 17.
- Apollo S-IVB- Apollo 13, 14, 15, 16, 17
- 1990's missions- Hiten, Lunar Prospector
- 2000's missions- SMART-1, Moon Impacting Probe, Chang'e 1, Chandrayaan-1, SELENE, LCROSS shepherding spacecraft, LCROSS Centaur,
Okay, on to the planets/comets/ etc!
- Scott and Amundsen- (Mars Impactors for the Deep Space 2 mission)
- Deep Impact- impacted a comet
- Galileo Probe - "Impacted" Jupiter, although there isn't really a Jupiter surface
- Galileo- After the end of it's mission, "impacted" Jupiter.
By my count, that's 2425 Lunar Impacting missions, and 5 others, for a total of 2930.
So, what reasons do they do intentional crashes? Here's some of the most common reasons.
- Most of the Apollo crashes were to assist in determining the composition of the moon. The Astronauts left seismometers on the moon, which the exact landing spot and time of an intentional crash allowed them to figure out the composition of the moon.
- Some crashed to create plumes, and figure out what was in them. Most of the later lunar probes (LCROSS, SMART-1, etc) have done this, plus the Deep Impact space probe. Some of these were an afterthought, as a mission was ending they wanted to get some value out of it, others were done as a primary mission.
- Some use the impact of the crash to try and get scientific instruments on the ground. These include MIP, and the Deep Space 2 missions.
- Some are done to prevent contamination. This includes the Galileo crash, as Cassini will also follow.
- Luna-2 was actually crashed as a propaganda strike, littering the surface with Soviet ribbons.
- The Ranger missions were designed to see the moon up close, for a very short period of time. They ended with impact of the Moon.
Some lunar missions (Quite a few) ended in less controlled manners. There is a finite lifetime for a Lunar mission, of only a few weeks to months without fuel. Missions weren't listed that didn't crash at a pre-defined time and place. LADEE for one is included in this list.