Top 10 Most Unexpected Deaths On Doctor Who

Danny Pink, formerly known as Rupert Pink, was known throughout Series 8 of New Who for being Clara Oswald's boyfriend. He even helped out the Doctor a few times. In the penultimate episode, Danny and Clara are having a conversation via cell phone; Danny crosses a street, when he suddenly stops speaking. Clara worriedly tries to talk to him to no avail. Suddenly, a different voice, the one of an aging woman, shakily informs Clara that Danny was run over by a car.
A little side note: Danny was later reincarnated as a Cyberman after exploring the Nethersphere. However, this was not a happy ending either, as he ended up back in the Nethersphere. He had the chance to send himself back into the world through a portal, but he instead sent a young boy he had accidentally killed while serving the military in Afghanistan.

Osgood, who first met the Doctor after a series of paintings in UNIT's gallery were broken from the inside, was a scientist who worked with UNIT. She later confronted Missy, a female incarnation of the Master, in the 3W Institute. They took the villain hostage inside Boat One, their personal ship. While she and some other UNIT members guarded her, Missy eventually rid of her restraints and killed Osgood and the other guards.
It is rumored that Osgood will re-appear in Series Nine of New Who.

Although it was implied that the Face of Boe was the aged and immortal Jack Harness, the Face seemingly met a final demise. The ancient being was kept in a special tank that helped him live, since he could not breathe in oxygen. In the year 500,000,000,053, his tank finally broke, causing the Face to die.
Legend had it that the Face of Boe would speak an ancient secret to an old friend. This friend turned out to be the Doctor, and the secret was "You are not alone," which predicted the return of the Master.

This was ne of the most eventful death on the show. I remember that one clearly.

Another member of the Preachers on a parallel Earth, Angela Price--better known by her alias, "Mrs. Moore"--worked with the Doctor in infiltrating the main base of Cybus Industries. While they were investigating a dead Cyberman, Moore turned her back--and was subsequently electrocuted by a Cyberman.

Okay, technically, she's not directly from the Doctor Who series. In the first episode of Torchwood, a BBC spin-off of the New Who series, a series of murders occurs in Cardiff in which the same weapon is used. At the scene of one murder, the Torchwood team used Suzie's "resurrection gauntlet" to briefly raise the victim from the dead. It turned out that Suzie was behind the murders and planned to use the victims as test subjects for her device. She attempted to kill Captain Jack Harness, not knowing he was immortal. His subsequent gunshot wound almost instantly healed, allowing him to kill Suzie. (She would come back to life--and die--again, but that's another story.)
It was later revealed that Russel T. Davies, who penned the episode, tricked viewers into thinking Suzie would be a recurring character and killed her for the element of surprise.
What a shame. At least this character deserved her death.

In an alternative universe, Mickey, a companion of the Doctor and boyfriend of Rose Tyler, was known as Mickey and was London's most wanted (for parking tickets). Belonging to a group called the Preachers, Rickey's goal was to warn the public of Cybus Industry's shady dealings involving kidnapping. On the night of his death, Rickey met Mickey and tracked down a Cybus unit to Pete Tyler's mansion, along with Mickey and his fellow Preachers.
Once there, they met with the Doctor, Rose, and Pete (Rose's dad, who died in her own universe) and fled from the invading cybermen. While trying to divert them away, Rickey and Mickey fled in opposite directions. They soon met each other again, only to be separated by a tall fence. While he tried to climb it, Rickey was electrocuted by a Cyberman.

On a tourist train on the crystal planet Midnight, the Doctor and a busload of other passengers were terrified when an unknown creature began knocking on the vehicle's walls and took over the body of Sky, one of them. The thing used the body to repeat the words of the other passengers, eventually hypnotizing the Doctor into repeating her words. Most of the other tourists thought the Sky had been freed and the creature was now inside the Doctor, but the Hostess knew that it was all a plan to escape getting killed.
In the end, the Hostess dragged the entity outside, where the planet was bathed in highly unstable UV rays; this caused the duo to disintegrate.
"The Hostess... What was her name? "--The Tenth Doctor

Imprisoned for killing her husband, the Master (a.K.A. harold Saxon), Lucy was eventually released--only to witness the resurrection of her evil husband using her biological imprint and a number of human sacrifices.
Oh, no! The Master is back alive with a vengeance! However, Lucy revealed that she prepared for this moment and she and some friends concocted an antidote that could reverse the effects of the resurrection rite. The explosion that occurred when the two substances combined destroyed the prison Lucy was being held in and killed everyone inside--including Lucy.
"Until death do us part, Harry! "--Lucy Saxon

This character was introduced in 1965 as a Greek maid who was taken into the TARDIS to be rescued from the ensuing battle famously known as the "Trojan Horse" battle. She then appeared in the next story, a whopping twelve-parter involving the Doctors' hated enemy, the Daleks, chasing the Doctor across time and space to acquire a special substance that would allow them to use a disastrous weapon, the Time Destructor.
At one point, the ship that the Doctor and friends were using crashed on the prison planet Desperus, where a weak prisoner named Kirksen boarded the ship and took Katarina hostage. In a final attempt to rid her friends of Kirksen, she opened the airlock, sending both of them into outer space.