Manipulator arm

The manipulator arm was a long, thin, mechanical arm found on most Dalek models, the exceptions being some Dalek Emperors' models and the Special Weapons Dalek-type model.

It is found in the right-hand socket in the Dalek mid-section, with the gunstick on its left.

Plunger
The ends of the manipulator arms typically are shaped like a plunger. For this reason, Dalek technology often has circular controls with which some can arm an interface by rotating clockwise or counter-clockwise. However, the black tip at the end, which gives the arm its "plunger" shape, can morph slightly to better interact with specific objects (such as finding the combination of electronically-locked doors). (DW: Dalek)

Even if the Dalek dies, its arm can still operate machinery if used by a live person (DW: Remembrance of the Daleks). The arm can optionally have a telescopic feature to enable the arm to extend outward. (DW: The Dalek Invasion of Earth, Dalek)

It could also serve as a weapon. Placed over the nose and mouth, the arm can generate enough hydraulic suction to suffocate and kill a Human and enough traction to more than crush a human skull or rip through sheet metal. (DW: Dalek, NSA: I am a Dalek) The Doctor claimed to have seen one crush a brick with ease. (NSA: Prisoner of the Daleks)

At least in the case of the Cult of Skaro, the arm could also scan brainwaves for information or act as a quick intelligence scan. (DW: Doomsday, Daleks in Manhattan)

Imperial Daleks had a more conical variant with a slotted rim specifically designed to operate imperial controls. (DW: Remembrance of the Daleks)

Claw
Alternatively, the arm can terminate in a mechanical claw with two or three pincers. A variation of that claw had eight pincers and was used to operate Dalek machinery.(DW: The Stolen Earth)

Flame-Thrower
Referred to by daleks as pyro-flames, these were small cylindrical pieces at the end of the arm which shot a stream of fire to clear swaths of forest. (DW: The Daleks' Master Plan)

Seismic detector (or perceptor)
A small device which looked like a compass suspended by gimbals, the seismic detector was employed to locate enemy time machines outside of the vortex. It could also detect approaching life-forms or the paths of fleeing ones, even through sealed doors. (DW: The Chase)

Electrode unit
The electrode unit, a device which looks like a radar dish, seems to be capable of remotely operating electronic controls. It was used in this manner to enter the Mechanoid City. (DW: The Chase)

Sieve
Kaled mutants are inserted into the dalek shell during assembly by a dalek fitted with a sieve instead of a plunger. (DW: The Power of the Daleks)

Syringe
One of the members of the Cult of Skaro exhibited an alternative attachment; a syringe. The syringe was merely fastened directly to the end of the manipulator arm in place of the plunger. (DW: Daleks in Manhattan)

Blowtorch
To cut through doors, early Daleks used a long thin instrument with two spheres and a clear disc set midway up. It isn't clear if this is held or directly attached to the arm. (DW: The Daleks) A later attachment was a small tip on the end which cut through metal as effortlessly as a soldering iron through plastic. (DW: The Planet of the Daleks) Assault Daleks had a claw and blowtorch combination. (DW: The Parting of the Ways);

Interface
Daleks that were within the Vault in the Crucible had a diamond shaped interface that was used to interact with machinery and technology within the Vault. (DW: Journey's End)

Cutting tool
The Daleks used a hot iron to cut through metal. On Spiridon they used one to cut through a thick door. (DW: Planet of the Daleks)

Alternative weapons
One alternative weapon was seen on two of the Emperor's Personal Guard. It appeared to be an upgraded Dalek gunstick, but slightly larger. The other side still possessed a gun. Another of the Dalek Emperor's guards had an arm with forward jutting silver protrusions on a small ball. (DW: The Parting of the Ways)