Many sites list “extremely powerful” builds, often with few if any entries that actually reach well into the limits of D&D 3.5e’s potential. Ultimately, there is a build that can have every stat as high as they choose to make it, and every ability in the game they choose to have, at 1st level—that would be Pun-Pun, and nothing is ever going to beat that for anything. Pun-Pun can have Epic Spellcasting1 and arbitrarily-high Spellcraft, so they can instantly create and cast an epic spell to do near-literally anything at all. Pun-Pun can also be an actual deity, and have any salient divine abilities they might wish—like alter reality.
To list anything else requires some kind of limitation that prevents Pun-Pun, because otherwise there’s no point in having anything on the list other than Pun-Pun. The traditional “theoretical optimization” limitation is “no infinite or arbitrary loops,” such as Pun-Pun uses to push all their stats into the stratosphere. This is, for example, the limitation put on the “Finite Values” section of the World Records Listing (which frustratingly lacks links to the majority of record-holders).
I have spent some time trying to find a version of the World Records with links, and cannot. I’m pretty sure there was, once, but so much has been lost to time. However, this Giantitp.com list of famous optimization builds looks to be fairly complete, and actually has links for a lot of stuff, huzzah! And minmaxforum’s Handbook Index is a must-see here—it’s got reasonably-practical guides for most classes, and a few theoretical optimization resources as well.
- Yes, an epic feat at 1st level. Dragons, man.