Building a Sage (3.5)

[Khedrac]

Or, more specifically, building a character who has optimized their Knowledge skills.

Race
This character is going to need to be Intelligence focussed, even if their actually classes are not, however we probably don't need to worry about this too much, a couple of extra points doesn't make a huge difference (no DCs) so we can go for something weird if it looks interesting to run.
First off - Human is always good with the extra skill point and feat.
Next up - grey elf, if we don't like the -2 Con then go for a dragonborn grey elf for -2 Str, +2 Int (and a hint of cheese).
Honourable mention to the dragonwrought kobold: -4 Str, +2 Dex but can abuse aging modifiers to start at Very Old (+2 Int) as they don't take the penalties (personally I would require the aging to be spread out across the character's levelling, so no bonus at level 1.)
Must mention in passing:
gnomes (all) for the feat to re-roll knowledge checks.
killoren - aspect of the ancient for +hit dice to Know: Nature, so +20 at 20th level...

Classes
Dragonfire Adept - take the draconic knowledge invocation to gain +6 to all knowledge checks, usable untrained. Only 4 skill points, but all knowledges on class list. Also, other class features can make the character quite effective even without optimizing Con for breath weapon DCs and Char for other DCs. Also, allows character to take draconic feats (see below)
Bard - obviously, but it can be nice not to use bard (or only dip).

Feats
Draconic Knowledge (DrM) - +1 to all knowledge skills per draconic feat +3 is pretty much automatic (dragontouched, draconic heritage X) but if you concentrate can get this to +5 or +6.
Draconic Aura: insight - another +1 to +4 (also boost allies), shame this does not appear to count as a draconic feat (you get the progression from being dragontouched).

Now assuming a 16 starting Int, with a +6 item, +5 from levelling and a +5 book that's a +11 stat modifier at level 20 (easily got higher).
Add in the auras and feats listed for another +9 and you are already looking at a +20 modifier for the knowledges with 0 ranks
With ranks you are looking at +41 (or +61 for a killoren on Know: nature)

So, what other sneaky tricks have I missed - this is very much a starting point as I see it.

Also, what items would you choose for a sage?

[haplot]

Could always try a cloistered cleric.

Not saying it be brilliant, but somewhat useable I think

[lylsyly]

Cloistered Cleric YES!!

6 skill points / level
All Knowledge Skills are class skills.
Free Knowledge Domain
Lore (just like bardic knowledge)

Play a sage type? Divination spells? Yes Please!!

[schreier]

I'd go Archivist deep imiskari I would think ... Only 4 skill points but built in knowledge abilities, and intelligence based casting.

Eventually go into loremaster

[gorfnab]

Some options to consider
Feat: Knowledge Devotion
Skill Trick: Collector of Stories
Magic Item: Tome of Worldly Memory
Prestige Classes: Urban Savant, Paragnostic Apostle

[Falontani]

Draconic Knowledge invocation is a +6 untyped bonus to spellcraft and all knowledge checks, only requires 1 level in Dragonfire Adept (and grants Dragontouched as a bonus feat)

Archivist has access to Dark Knowledge (something thematic that grants bonuses to allies for using knowledge checks) while also 4+int mod skills, int spellcasting, and all knowledge skills as class skills. It also gets Lore Mastery which is +2 to a knowledge skill of your choice, and you get it again at levels 7, 13, and 17.

Dream Dwarf gets +1 CL with Divination Spells

Spellgifted gets +1 CL with a school of choice for -1 CL of all other schools (and can choose Divination)

Divine Oracle grants the Oracle Domain, which grants +2 CL for the Divination school; the class is also thematic and progresses divine spellcasting, which will likely be this character's secondary focus

Divination Domain grants +2 CL for the Divination School

Knowledge Domain grants +1 CL for the Divination School

Keeper of Forbidden Lore feat grants +1 knowledge (the planes), spellcraft, and Bardic Knowledge (or lore which works as bardic knowledge) per abyssal heritor feat you possess

Unseen Seer is a fairly thematic choice, granting +3 CL to the divination school as well as adding several divination spells to a spell list that normally doesn't possess them.

Visionary Seeker is a thematic choice, granting +1 CL to the divination school per level in the class, 4+int skills, and all knowledge skills as class skills (again), however it unfortunately is a fairly weak class and only grants 1/2 spellcasting progression

The Dantallion Vestige grants +8 on all knowledge checks, is fairly thematic, and grants the ability to Read Thoughts at will

Ancestral Knowledge allows you to make all knowledge skills Wisdom based instead

[daremetoidareyo]

House of knowledge petitioner keeps all knowledge skills from their life. Put human heritage on that. Spellscale that bad boy at 2HD so you can keep all your knowledge skills. So, elderbrain mindflayer > petitioner> spellscale then start adding class levels.

Dig around here: https://forums.giantitp.com/showthread.php?514547-The-Library-of-Knowledge-Getting-the-most-out-of-your-studies

[Rebel7284]

Factotum is nice for this. 1/day/skill you can add your Factotum level to a skill. Plus you have access to some spellcasting, so can boost this with spells.

Incidentally, Sadism and Masochism with enough prep time can be used to generate arbitrarily large skill checks if you want to be cheesy about it. Looks like you are looking for non-cheesy options though.

[Khedrac]

I agree think that if you are going for the spellcaster route Archivist beats Cloistered Cleric - simply by being Int focussed; they also get the their class ability.
Cloistered clerics get more skill points and domains, and large boosts to divination spells =/= being good at knowledge skills.

So dream dwarf - not as good as the races already postulated, but their ethereal vision is nice.

Keeper of the forbidden lore - good call and choice for know. planes specialists.

Dantillion vestige - I had not even considered vestiges - very nice suggestion - stack this with 1 level of DfA and the boosts just keep climbing!

The problem with Ancestral knowledge is that there are now multiple options listed that give bonuses based on the number of feats of a certain type possessed, so any feat not of that type has to give a better bonus. That makes this feat good for a (cloistered) cleric-based sage, but a waste of time for anyone else.

I looked at the feat knowledge devotion - and unless you personally will be hitting the enemy it's a waste of time for a sage.

Library of Knowledge post link - thank-you for that - I expect to spend far too much time in there in the near future!

What we need is more magic items!

And how did I forget the skill trick I have used on previous characters...?

[Eladrinblade]

Grey Elf Bardic Sage, obscure lore feat, ranks in every knowledge skill and spellcraft (and probably perform). Cloistered cleric gets the knowledge domain though, which is also pretty fitting.

[Kalkra]

One level of Warlock will let you double up your Knowledge invocations.

[Ruethgar]

Master Class(Dragonlance), Sage route can give you Academic Reputation to make a convincing scholar that people would actually listen to without Cha. Lore also makes Master levels stack with Bard for Bardic Knowledge. Of course all Bloodline levels can be taken free of cost as written to boost your effective class level for knowledge sky high as well as just about remove the potential for you to max out ranks in your knowledge skills. Exploit Weakness for Int to attacks and Tactical Advantage for pseudo-Knowledge Devotion if you wanted a Robert Downey Junior style Sherlock.

Also, Lucid Dream into being a Legendary(also the Master class) specialized library of anything. Can't recall off hand, but I think specialized libraries are a +6 circumstance, Legendary makes that +30. Have to dream for it, but still.

All of this aside, the Omnisipher knows everything in their selected fields at level 3. I can't recall the combination, but they get true infinite(as opposed to Pun Pun's neigh infinite) bonuses to a handful of skills.

Wish to be a Giant but fail changing anything except the type then ritually add Primordial Giant for more Int.

[daremetoidareyo]

There is a class in dragonlance campaign setting that allows you to add ranks in concentration to an int based check. Inquisitor.