The highest skill check modifier you've ever seen (or built for) in a d20-based game?

[RhoTheWanderer]

Pretty much what it says in the title.
A little bit of background: I'm running an "Evil" campaign of sorts using d20 Star Wars. We have a few force users leaning strongly toward the dark-side, a bounty hunter, and a noble that I allowed a player to run in addition to his main character (to facilitate some background issues and a bit of social stuff).

The synopsis is that they're somewhere between 7000 and 4000BBY and their accomplishments (along with some other things I may concoct) won't be found in the historical record as it was just mysteriously absent from any of the jedi/republic/sith/ect archives (possibly due to deliberate deletion or an accident or what-have-you). They're basically gonna take over the universe, probably making Death Stars way ahead of their time in the process, and create a great sith empire.

One player has recently voiced the desire to create a massive slave-trade business. Now, once they have (at least temporarily) overthrown the Old Republic and declared themselves supreme rulers or something, they could easily legalize slavery. But until then, I'm thinking of having it be that any skill checks related to conducting slave trade in the galaxy would be as follows:
Core=Virtually impossible. Must be at least level 20 and be focused on any related skills and roll a few natural 20s (or other high numbers if you work out a clever plan that takes years in the game world to set all the pawns and details into place) to stand a chance of pulling off a deal and getting away with it.
Inner Rim=Easier than Core worlds. By levels 16-20, with good rolls and devoting a few resources you could pull off a deal.
Outer Rim and Beyond=Fairly Easy. The DCs would be easy, but actual profit would be minimal due to how easy it is to come by slaves out there.
Mid-Rim=Difficult, but possible (and profitable) for low- to mid-level characters with decent rolls and a little bit of charisma or the right skills/feats/classes.

But then I got to thinking, "Considering the ridiculous skill check-boosting shenanigans that can be accomplished in 3.0/3.5, what actually constitutes an 'Impossible' skill check?"
Doesn't matter if you're coming from D&D(3.0/3.5), Pathfinder, d20 Modern, d20 Star Wars, or something else based on the d20 system. But what's the highest skill modifier/check you have ever seen in-game? What's the most optimized skill modifier for which you have ever built (preferably at level 20 for comparison purposes, but feel free to show level by level or just a specific level(s) if you like)? What are the ways that you have used to boost your skill checks? Have fun people!

[AvatarVecna]

Largest skill checks I've ever seen, whether in a real game or in theoretical optimization, is Jump checks: every 10 ft beyond 30 gives +4 to Jump checks.

As for theoretical optimization, have you heard of the Jumplomancer? It takes advantage of the Exemplar ability to use any skill as Diplomacy, and then jacks up Jump and speed so high that it can hit the 150 for turning someone from Hostile to Fanatic.

[Wacky89]

I think it was me playing a awakened dark creature hairy spider.
Hide of +50 at level 5

[Taveena]

The Omnificer is a TO build designed to beat Pun Pun. Using an infinite damage loop and the ability to turn damage taken into a bonus to skill checks, they manage an infinite bonus to all skill checks. At level 4.

[Bluydee]

I once got my Handle Animal check high enough to tame the Phaethon in the ELH.

[Heliomance]

I built a character that didn't bother picking locks because she could make the Escape Artist DC to crawl through them instead.

[Necroticplague]

For actual games, (not counting a theorycrafting experiment on this site similar to the stuffy doll) I currently am playing a character that has +75 to concentration without any buffs. This is due to feat that gives+4 to CHA skills, Marhsal Inspire Charisma, and being undead (which makes concentration base on charisma). And a Charisma of 56. After buffs (including boosting charisma and flat out bonus to concentration), its a good 119. Well above the dc 40 for the thing I actually got the skill for (using Extraordinary Concentration for a 5th level spell for swift-action concentration). Thus, reason that character also picked up Insightful Strike, turning that check into damage.

[NichG]

I was in a campaign where you could craft magical items without the requisite feat, spells, or xp cost if you were able to hit extremely high Craft checks. At one point we were making maybe +10-+12 equivalent gear through a combination of gimmicks across the party letting us hit Craft DCs around 300 or so. It was very much an anything-goes campaign aimed at pushing the system as far as we could short of breaking (though anything infinite or 'arbitrarily high' was explicitly restricted)

The net trick combined a crap-ton of stuff - open-ended stat boosts via Owl's Insight fed by caster level boosts, combined with X-stat-to-Y shenanigans. Item Familiar. Marshal auras. Magical locations. Broken Faerunian magic items that gave a stacking bonus. Stuff from obscure d20 sources (Star Gate d20) allowing aid-another which scales with how good the aiding character is at the skill. Tons of homebrew.

We probably could have pushed it quite a bit further by the end of the campaign, but the character with the gross stacking aid-anothers ended up getting swapped out for a new character without the trick, so we lost a big chunk of the bonuses.

Generally speaking, I assume that optimized PCs will eventually be able to hit about 100-120 in a skill check in a normal D&D campaign by Lv20 if they really have a good reason to do so (e.g. they're willing to dedicate a significant portion of their character to that one trick). Most of the stuff required comes online pretty quickly, so they can get most of the way there by Lv10 or so.

[Phelix-Mu]

I believe Piggy Knowles hosted a build challenge on this site to see how big a Diplomacy bonus could be stacked without using infinite loops or omniscifier-grade cheese. I believe the final result was north of +250, and that was after quite a bit of book-diving. You can probably find the thread using the forum search function, assuming that Piggy was actually the one that hosted the thing.

So, yeah, in an actual campaign, +100 is not that hard to get for a player with good system mastery and access to all sources. In general, the epic DCs from the Epic Level Handbook were laughably easy to meet.

[The Viscount]

The highest numbers I've seen that aren't simply (arbitrarily high number) like with the Omniscifier are those of Wasy the orbital basket bombadier. It's a TO joke build, but it's legal, and gives a result of 1107-1177 on craft (basketweaving) and 230520-288190 on jump.

[FearlessGnome]

The antimagic-proof assplomancer. (http://www.giantitp.com/forums/showthread.php?238255-New-amp-Improved-Assplomancer) Have not quite found the game for it yet.

[Smegskull]

I have a character with a + 18 to move silently at lvl1 with no items so I could quickly bump that to +33 with armour buffs