I'd add Jason Butler on Pierce The Veil's Tangled In The Great Escape, Kelling Quinn on Pierce The Veil's King For A Day, and Justin Pierre and Patrick Stump's appearance on Chicago Is So Two Years Ago and Everything Is Alright, respectively.
I mean, Fall Out Boy are pretty good with these.
Foxes and Elton John on their SR&R songs (I also really like Courtney's spot).
Brendon Urie on 20 dollar nose bleed. And all of the guest on What A Catch Donnie.
Butch Walker (his line is delivered so well) on You're Crashing.
The one on TTTYG with the guy from MCS.
I really don't care for the guest on FUTCT though.