The 3.5 Shapechange Handbook

[jmax]

In general I only add things that provide earlier/easier access or better features than what I already have. The point isn't to list every possible form - it's to list every form you'd specifically want to use, within reasonable constraints. Unless it's super awesome fluff-wise, that means it has to be better mechanically, lower level, or from an easier book. Otherwise it's both extra clutter and an unnecessary performance drop for users with low-end hardware.

My goal here is to cover everything one might want to do with shapechange rather than anything one could do. In that spirit, I have omitted creatures whose abilities are inferior to others with similar abilities unless they have other important qualities, such as an overall stronger form, better mobility or defenses, or a more accessible sourcebook.

Shadow Dragon (Draconomicon) has Shadow Blend for total concealment outside full daylight or a daylight effect. Also, energy drain immunity and a level draining breath weapon!

Energy drain immunity is easy to come by - all undead and constructs are immune.

Shadow Mastiff is core and provides an identical ability, albeit on a weaker chassis. Shadesteel Golom is from a more accessible book, available quite early, and has a very nice chassis as well.

The level-draining breath weapon is interesting, but the save DC is bad. Probably worth listing anyway given the decent area and targeting Reflex - it fits the "many creatures" criterion at a minimum.

In order to be listed here, a debuff must either affect a very large number of creatures, be a free action or non-action to use, have no save (or occasionally a Reflex save), or possess some other unique and very powerful attribute. There are so many potent disables available with shapechange that debuffs just aren’t that spectacular.

What I do like with the Shadow Dragon, and this is definitely worth listing, is the hour-long, 300-ft-radius cloud of perfect darkness it can produce three times per day and then hide in at will while seeing normally - though I might switch to a different shadowy form depending on what I want to do.

Tarterian Dragons (Draconomicon) have continuous (Su) freedom of movement, just in case you want to slip into that form to slip out of something.

Tarterian dragon doesn't offer much that I don't already have from more accessible forms. Spider Eater is core and provides continuous Freedom of Movement at any caster level. At high caster levels, Storm Giant (core) and Hound of the Hunt (much more commonly allowed source) are better in almost every way. There's a brief period at CL 17-18 in which Tarterian dragon is better for simultaneous defense; aside from that, the only thing it brings to the table is faster flight. I'll probably list it anyway for those reasons, but it's pretty narrow.

Draconomicon, Monster Manual V, the Fiendish Codexes, Elder Evils, Manual of the Planes, Planar Handbook, Monsters of Faerun, and the Eberron/Faerun books in general seem like handy places to check for forms.

I've done MM5, Fiendish Codexes, Monsters of Faerun, and I think Manual of the Planes. The rest are somewhat lower-priority sources for various reasons, including both obscurity and setting limitations. I may take a pass through the rest at some point, but I've been mostly working on other projects lately, so I probably won't be spending multiple consecutive days crawling through books page by page in the near future.

Why do you so highly value Prismatic Golem form? What about its moral code (Ex) SQ?

Moral Code is not an Ex or Su ability, so it does not come with Shapechange. Even if it did, the literal wording says it stops obeying its creator if given conflicting instructions. There's no creator and no instructions, so it's irrelevant.