This is a possibly amusing build I threw together over the past couple hours. It achieves an Initiative modifier in the 50's and higher, but there are some possible rule twists needed to achieve this feat.
1: A Factotum's Cunning Strike counts as Sneak Attack for prestige qualifications. Nowhere in the rules does it say it can't be used as such.
2: Cunning Strike can be stacked up to at least 2d6. Most people agree that only getting a max of 1d6 is BS, especially on a single attack.
3: The class features of untyped Intellect to initiative stack. You'll see what I mean with the build.
4: Trapsmith's Haste counts for Swiftblade entry. The authors themselves noted they'd have rewritten Swiftblade's "must have used every 3rd level spell slot on Haste" in lieu of the Trapsmith.
Now for the build:
Race: Human
Alignment: Any nonlawful
Deity: Any
Classes: Factotum 5/Trapsmith 1/Swiftblade 4/Bayushi Deceiver 2/Exemplar 8.
28-point buy
Starting Ability Scores: STR [10], DEX [13], CON [10], INT [18], WIS [10], CHA [9] Dex is for the prereq Dodge and Int is for everything else. Int will go up to 23 with levels, 28 with a Tome, and 34 with a Headband of Intellect for a +12 Intelligence score.
Feats:
Human: Improved Initiative
1st: Dodge
3rd: Mobility
6th: Skill Focus (any)
9th-18th: Any. Might as well go with FoI, Knowledge Devotion, etc. Travel Devotion would work well with the overall design.
Needed skills:
Trapsmith: Craft: Trapmaking 8 ranks, Disable Device 8 ranks, Open Lock 5 ranks, Search 8 ranks.
Swiftblade: Concentration 6 ranks, Spellcraft 6 ranks
Buyashi Deceiver: Bluff 8 ranks, Diplomacy 8 ranks
Exemplar: Diplomacy 6 ranks, any other skill 13 ranks
All of the 8 and under skills can be had by a 5th level Factotum with more skills to spare. The Exemplar's 13 ranks can be in any skill besides Diplomacy.
Now for why this build gets a 40+ Initiative modifier:
Dexterity to initiative: +1
Improved Initiative: +4
Factotum 3: Brains Over Brawn grants Intelligence to all Strength and Dexterity checks, including initiative. +12 at 20th level.
Swiftblade 4: Arcane Reflexes grants a competence bonus on initiative rolls equal to the arcane spellcasting ability modifier. That's Int, for another +12.
Buyashi Deceiver: Strike First, Strike Last means a Bayushi deceiver of at least 2nd level adds his intelligence modifier to his initiative checks. +12 again.
Exemplar 8: Intellectual Agility lets an Exemplar add his Intelligence bonus to initiative checks and Reflex saves. +12 yet again.
With only class skills and two items, this character has +53 to his initiative checks. Add in an Eager Warning weapon for +7. We're at an even 60 now. Top it off with Nerveskitter's +5 for +65 to initiative. Primal Senses wouldn't work because it's a +5 competence bonus, which is overwritten by Swiftblade's bonus.
Just for the heck of it, here's total BAB, base saves, and base skill points. I'm not including stat gains from the Tome of Clear Thought into the skill points since it's already kinda silly being able to max 12 skills by level 20.
Factotum 1: 0/ F0/R2/W0 44SkP
Factotum 2: 1/ F0/R3/W0 55SkP
Factotum 3: 2/ F1/R3/W1 66SkP
Factotum 4: 3/ F1/R4/W1 77SkP
Factotum 5: 3/ F1/R4/W1 88SkP
Trapsmith 1: 3/ F1/R6/W1 99SkP
Swiftblade 1: 4/ F1/R8/W3 108SkP
Swiftblade 2: 5/ F1/R9/W4 118SkP (Intellect bump to skills)
Swiftblade 3: 6/ F2/R9/W4 128SkP
Swiftblade 4: 7/ F2/R10/W5 138SkP
Buyashi D 1: 8/ F4/R12/W5 150SkP
Buyashi D 2: 9/ F5/R13/W5 162SkP
Exemplar 1: 9/ F5/R13/W7 176SkP
Exemplar 2: 10/ F5/R13/W8 190SkP
Exemplar 3: 11/ F6/R14/W8 204SkP
Exemplar 4: 12/ F6/R14/W8 219SkP (Int SkP bump)
Exemplar 5: 12/ F6/R14/W8 234SkP
Exemplar 6: 13/ F7/R15/W9 249SkP
Exemplar 7: 14/ F7/R15/W9 264SkP
Exemplar 8: 15/ F7/R15/W10 279SkP
Using partial BAB combination, BAB would go up to +16 and allow for the extra iterative. Thanks to base Dex and the Exemplar's Intellectual Agility, he's now at +28 to Reflex saves. Ring of Evasion, anyone?