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 looks like a compass suspended by gimbals, the seismic detector is employed to locate enemy time machines outside of the vortex. It can 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)

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)