Gnasty's Loot. This music perfectly embodies the stage's "You've pretty much reached 100% Completion, Spyro. But it's not over, you're almost there: your final stretch is going to be fun." kind of feeling.
Dark Hollow. Despite its name, it's an amazingly calm theme for a nighttime stage, and almost manages to evoke some kind of "summer nights" feeling.
Wizard Peak. This kickass BGM, just like Gnasty's Loot above, has a very "Let's have fun!" feeling.
Even though it was a brutal That One Level, Tree Tops had incredibly fitting and awesome background music. The way the music seems to climb towards the middle before dropping back down perfectly captures the feel of those supercharge challenges that we all love so much.
The main theme of Spyro the Dragon, heard on the title screen, and its moody remix heard in Toasty and the Gnorc Gnexus.
The credits theme for the trilogy is the same across all three games, and is particularly catchy as well as helping to tie all the adventures together. The Year of the Dragon credits, with the classic theme, are particularly bittersweet, given what happened next.