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. Varriants 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
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)

New Series (Series 5)
 'This has been written after me just watching the episode. Please correct if wrong, but remember that THIS MAY CONTAIN SPOILERS.' 

In the New Series 5 episode Victory of the Daleks the latest Daleks (referred to as the "Supreme Race") are wider behind, come in different colors (the 6 shown in the episode are white, green, red, yellow, blue and orange), have an orange glass on the eyepiece instead of the regular NSD blue with 8 sharp black points coming out of the eyestalk. They also have more powerful lasers which completely disintegrate victims instead of the regular NSD laser. The new Daleks also destroy "inferior" Daleks (the green camo and original NSD Daleks on the ship were destroyed). (DW: Victory of the Daleks)