Dalek variant

While the basic appearance of Daleks have remained the same throughout their history, there have been several changes and alterations from Davros' original design of the Mark Three travel machine. Variants on the 'basic' Dalek design have been redesigned both by Davros and the Dalek Emperor/Dalek Supreme (these two representing the major power holders in the Dalek heirachy). Both factions of Daleks have in common a Standard Dalek used for basic combat.

A Dalek variant should not be confused with a Dalek using a different Manipulator arm as these are not considered true variants.

Davros' Variants
Early in his design work Davros created Spider Daleks, which walked on a set of spider like legs, rather than gliding accross the ground, these were succeeded by Daleks known as 'Strider Daleks'. (EDA: War of the Daleks)

Following his awakening from cryogenics and an encounter with the Dalek Supreme Davros set up a base of operations on Necros and began creating Daleks of Human Origin as the name suggests these Dalek variants were created using humans, rather than Kaled mutants. This process also employed a Glass Dalek. (DW: Revelation of the Daleks)

Dalek Emperor / Dalek Supreme variants
The Dalek Emperor and Dalek Supremes were marked out as having several different designs apart from other Daleks, however they also created altered designs under their own command.

Under the command of a Dalek Emperor the Cult of Skaro were created. (DW: Doomsday)

Shared design variants
Both Davros and the Dalek Emperor have been known to use Special Weapons Dalek variants in combat situations, Davros utilised one during the Shoreditch Incident whilst the Dalek Emperor utilised several campaigns. (DW: Remembrance of the Daleks, DWM: Fire and Brimstone, EDA: War of the Daleks)

Post-Last Great Time War
Logic suggests that the gold Daleks would be the 'MArk IV', and the Progenitor Daleks the 'Mark V'. Following the Last Great Time War several new Dalek variants were created, both embryos, not technically a variant, but rather an attempt to recreate the original Kaled mutation. (DW: Daleks in Manhattan)

Following Dalek Caan's intervention, a new Supreme Dalek was created, along with Vault Dalek to guard and maintain the vault of the Crucible. (DW: The Stolen Earth)

After the apparent eradication of the Dalek species as a whole (DW: The Stolen Earth) a small, ragtag group of Daleks found themselves stranded into the Second World War era, where they concocted a plan to have the the Doctor identify them as Daleks to the Progenitor, an ancient Dalek instrument containing samples of the original, long-lost, Kaled DNA. The Progenitor created five new specimens, along with five larger and colour-coded cases, named "Scientist", "Strategist", "Drone", "Eternal" and "the Supreme". The New Paradigm Daleks proceeded to destroy their degenerate descendants/forebearers and fled to parts unknown to start anew a restored Dalek Legacy. (DW: Victory of the Daleks)