I'll try to make a list of the songs you can find in the game

Note that the game uses MIDIs

• Main Menu / Sound Test Track 1: Tengu Man - Mega Man 8 (Sega Saturn) / "Ruined Area" - Intro Stage - Rockman 8: Metal Heroes / Maelgrim http://maelgrim.tripod.com/Rock8mus.html

• First cutscene / Sound Test Track 2: Panic Puppet Zone Act 1 - Sonic 3D Blast / Twinkle Cart - Sonic Adventure

• First cutscene / Level 5 cutscene / Sound Test Track 3: Round 3 - Forest Fortress - Area 88 / U.N. Squadron (Capcom)

• First cutscene / Sound Test Track 4: Unknown, could be from Final Fantasy, the music has similarities with Go Above the Clouds! - Final Fantasy III

• Level 1-1 / Sound Test Track 6: Super Mario Bros. 1 Overworld - Super Mario All-Stars

• Level 1-2 / Sound Test Track 7: The Kids Aren't Alright - The Offspring

• Level 1-2 (skateboarding) / Sound Test Track 8: Sector Alpha/Sector Beta/Rainbow Road - F-Zero X

• Level 1 End cutscene / Level 3 End cutscene: Super Mario Bros. 1 Overworld (Remix)

• Level 2-1 / Sound Test Track 5: ENEMY: CHAOS (or Boss: CHAOS ver. 6) - Sonic Adventure

• Level 2-2 / Level 4-2: Venus' Theme - Sailor Moon S (Game)

• Level 3-1: Hitohira, Kasumi's Theme - Dead or Alive 2

• Level 3-2: "untitled", MIDI by Paul Lapensee, 1997

• Level 4-1 / Sound Test Track 9: Shade Man's Stage Theme - Mega Man 7

• Level 4 End cutscene: Underground Theme - Super Mario World 2: Yoshi's Island

• Level 5: Bowser Theme - Super Mario 64

• End Credits: Sha-La-La-La-La - The Walkers

• 2 Player Mode: Hammer Bros. Battle Theme - Super Mario Bros. 3

--- Found in code but unverified (looks like some of them are unused):

• "Sapphire City Act 1"
• "Dark Ambience"
• "mgzr7egb"
• All I Want - The Offspring
• Sonic Rush Adventure - Mystery Island