List of (almost) all way to change form!

[Condé]

Added Yuan-ti purebloods. Alter Form at will into Tiny to Huge viper.

Missed that it was a player oriented guide my bad. I did find some more options for players though
Unyielding Form of Inevitable Death (CMage)
Dreaded Form of the Eye Tyrant (CMage)
Anarchomancer PrC (Not arachno, anarcho)

And... Added. Thank you very much.

Some more stuff...

Races:
Fey'ri (Races of Faerûn) - Alter Self (any Humanoid form); LA +2 (but Lesser Planetouched rules...)
Gnome, Svirfneblin (Underdark) - 1/day Disguise Self; LA +3
Gruwaar (Dragon #317) - 1/day Disguise Self; LA +0
Irda (Dragonlance Campaign Setting) - Change Shape (any Humanoid creature; 3/day); LA +2
Seawolf (Stormwrack) - Change Shape (human or a wolf-human hybrid); LA +2 and 4 HD
Tibbit (Dragon Compendium) - Feline Transformation
Worghest (Dragon #350) - Change Shape (wolf); LA +2 (but Lesser Planetouched rules...)

Templates:
Half-Doppelganger (Dragon #313) - Alternate Forms (three Humanoid forms of Medium or Small size); LA +2
Magic-Infused Creature - Minor Polymorph; LA +1

Classes:
Corrupter - NE Paladin variant (Dragon #312) - at 3rd level, Disguise Self Cha mod. times per day (CL = class level)
Mimic - Rogue ACF (Exemplars of Evil) - at 1st, 3rd level, 6th, 9th, 12th, 15th, or 18th level, Disguise Self 1/day (+extra uses by reducing the Trap Sense bonus)
Psion (Egoist) - Change Shape

PrC:
Acolyte of Ego (Tome of Magic) - Cadence of the Secret Mask (Disguise Self for 1 minute per class level)
Eye of Lolth - non-Drow adaptation (Drow of the Underdark) Disguise Self at 3rd level, Alter Self at 6th level, and Polymorph at 9th level
Faceless One (Dragon #300) - at 2nd level, Disguise Self at will; at 5th level - Alter Self at will
Fiend of Corruption (Fiend Folio) - Alternate Form
Mortal Hunter (Book of Vile Darkness) - Mortal Skin
Psion Uncarnate - Assume Likeness
Scar Enforcer (Races of Destiny) - Disguise Self (Elf or Human)
Spy Master (Complete Adventurer) - Cover Identity
Tiger Mask (Dragon #300) at 5th level - Alter Self 1/day
Zhentarim Spy (PGTF p.78): Cover Identity

That's a lot. Not too found of Dragon Mag, so there is big chance I missed these.
I would argue Spymaster does not qualify since nothing change its appearance. It just obtains a bonus on its disguise skill. Same for Zhentarim Spy.

Two more (old favourites of mine):
1. Mountebank^DComp; gets Infernal Guise (Sp) at level 4, which is essentially Alter Self for up to 1/2 mountebank level + CHA modifier number of days;
2. Mountebank^CS; gets an Alter Ego (Sp) at levels 3, 6 and 9, which is essentially Altrer Self at will, but the mountebank can only assume one specific form with each instance, ending up with four forms they can switch between at will at level 9.

Edit: Deepwyrm drow and half-drow^DrM have Disguise Self as a 1/day SLA; if the lesser version is used for drow, both are LA +0.
Edit (again): The Tainted One^RoF template (LA +2) gives Polymorph (into viper forms only) as a 3/day SLA; Yuan-ti can do the same at-will, but it comes with alot of RHD.
Edit (again): Slyths^Und (LA +2, no RHD) have an Alternate Form (Su) ability. They can turn into an amorphous puddle with it.

I saw your post after the Yuan-ti addition. I agree it is barely for PC but I still added for completion sake.

Ninja Spy (OA) gets Alter Self at will.

Aaaaand... Added! Thanks.