Is there any comprehensive list of buff spells from all D&D 3.5e sources out there?
Not legally, anyway. The overwhelming majority of 3.5 spells are from non-open content, and therefore cannot be reproduced by a website to allow for searching, indexing, filtering, and so on. Only Wizards of the Coast is legally able to provide such services, and they have not done so.
The closest you will come is probably imarvintpa’s Dungeons & Dragons Spells Live, which is a remarkably-comprehensive listing of spells and related features. However, in an effort to remain compliant with copyright law, minimal details about each spell are provided.1 You won’t find the complete rules (except for those that are open content), and there is no official “buff” designation. Still, doing a Find Spell search checking off the various “harmless” options, or searching for personal-range spells, will probably get you closer to your goal than any other source.
- I am not a copyright lawyer, and I do not know if the details provided are sufficiently minimal to actually be compliant with copyright law. That said, imarvintpa has been around for a long time, and many copyright-infringing sites have been issued cease-and-desist letters in that time while imarvintpa (apparently) hasn’t, so it seems that Wizards of the Coast has either somehow missed it, or is OK with it.