The last track of the soundtrack album, titled "The Incredits" (there's that Giacchino wit), is a wonderful suite of themes and just pure awesomeness. I do remember reading YouTube comments that said someone else composed this track, however. I hate the prominence of ghost writing in modern film scores and always try to give credit where it is due; I want to be able to appreciate Giacchino's work as an artist, and in order to do that I need to listen to HIS work, not some other guy. Because personally, Incredits is my favorite track on the album, and if Giacchino didn't compose it then I can basically say that he isn't as incredible as I thought he was. This track is excellent and whoever actually composed it deserves my mental recognition.

So did someone else compose "The Incredits"? Or was it good ol' Giacchino?

T'was Giacchino.

He won an award for the best arrangement. I think it was for that track alone.

I've heard The Incredits was composed by him but he bought someone to arrange, at least the band part, I have no idea but the composition was definitely his, as it contains some of the themes he composed for the film

The Incredibles (2004) - Michael Giacchino
Orchestrated by Tim Simonec, Jack Hayes, Adam Cohen, Matthew Ferraro, Chris Tilton, Gordon Goodwin
All tracks were written by Giacchino.
Tim Simonec was the main conductor/orchestrator.

1m1v1 Disney Logo Music
1m1v2 Disney Logo Music
1m2 The Incredibles
1m2Rev The Incredibles
1m3 Elastigirl
1m3Rev Elastigirl
1m4 Rush Hour
1m4Rev Rush Hour
1m5 Trainschtupping
1m7 Incredible Wedding
1m8Rev Newsreel!
1m10 Violet's Crush
2m1 Paladino's Missing
2m2A Going Bowling
2m2B Rev Jewelry Store
2m4s Incredible Muzak
2m7A Incredible Again A
2m7B Incredible Again B
2m7C Going Bowling
2m8 Some Kind of Mirage
2m9 Bob Can't Help Himself
3m1&2 Incredible Again
3m3 Bob vs Omni Droid
3m4 Dinner with Mirage
3m5 Life's Incredible Again
3m5 New Off to Work
3m6 New and Improved
3m7 I'm Syndrome
3m8 Incredible Getaway
4m1/2 Bob Sneaks In
4m3 Bob's in Trouble
4m4 Bob's Imprisoned
4m5Rev Missile Lock
4m6 A Confirmed Hit
4m7 Heading for Land
4m8 Violet's in Charge
5m1 Helen Sneaks In
5m2 Launching the Omni Droid
5m3A Rev Intruder Alert
5m3B Rev 100 Mile Dash
5m4 Rev A Whole Family of Supers
5m5/6 Capture and Escape
6m1 Road Trip
6m2A Incredible Battle
6m2B Rev Incredible Battle
6m3 Rev Incredible Success
6m4 The New Babysitter
6m5 First Date
6m6
6m8 Bob's New Record
End Credits and Crawl (Revised)
Overdubs

Just for the record - it was Gordon Goodwin who arranged the Incredits. Meaning, Giacchino provided him all the themes and motifs so that Goodwin could add his handwriting and arrange the cue we got. There are a few interviews where Michael explains it.