The entirety of Splash Mountain and the Haunted Mansion. The descent from the Irons version of SSE.The entirety of the original Universe of Energy. The Land's area music loop. The Festival of The Lion King (cheating because it's a movie soundtrack )
I love Country Bears so I enjoy Blood on the Saddle even though I know it's a cover. I also like the entire Tiki Room show music, Grim Grinning Ghosts, POTC, the Splash MTN sound track, and the odd assortment of space like sound effects in SM.
My favorites are "You Can Fly", "There's a Great Big Beautiful Tomorrow", "Beat Time of Your Life"/"Now is the Time"?, and "Zip a Dee Doo Dah". "Mama Don't Whoop Little Buford" is always a fun one too.
I love coming into the "cave" with all of the animals singing, and me singing along like a dork with my head turning from side to side as I try to take it all in. Any day at WDW is a wonderful day!
The tunnel music at Space Mountain. It's just so eerie and along with the dark tunnel, the lit up signs, how iconic the ride is and the ambiance of the whole idea of the ride makes it one to remember forever in my opinion.
I really like way too many to choose...
One Little Spark
Spetromagic
Wishes
Great Big Beautiful Tomorrow
Star Tunnel
Soain'
(And if Disneyland counts...Paint the Night)