Out of curiosity, I wanted to know if there were any acts that appeared on the first and last AT40s for each of the show's hosts (Casey, Shadoe, and I suppose eventually Ryan). Thanks to Shannon Lynn's link, I checked the archive of Walt Bailey's website to find out.
First and last Casey AT40 (first run):
* The Moody Blues ("Question" and "I Know You're Out There Somewhere")
* Michael Jackson (The Jackson 5's "The Love You Save" and "Another Part of Me")
First and last Shadoe AT40:
* Aerosmith ("Rag Doll" and "Blind Man", plus "Love in an Elevator" was an extra on the last show)
* Gloria Estefan ("1-2-3" and "Turn the Beat Around")
I also checked Casey's first and last Casey's Top 40, as well as the last Top 40 Countdown which aired four weeks after Casey's last show, but there were no acts that appeared on both shows in either case. However, the last CT40 (airing two weeks after Casey's last show as host) had Cheap Trick's "The Flame" as a Request and Dedication, while Robin Zander had "Surrender to Me" on the first CT40.
Walt Bailey's site didn't have info on the last Casey AT40 (second run), or the first and last AT20 and AT10 (including the Westwood One years).