Now, while the songs past me showed are all SUPER-GOOD, he's pretty wrong. Since I can't order them well, let's just go through some great songs from games. I'm sure I'll forget some.
Calling to the Night, from Metal Gear Solid: Portable Ops (also featured in Super Smash Bros. Brawl)
Portable Ops wasn't a very good game, but Calling to the Night is fucking awesome. All three Big Boss games have AMAZING themes, including
Heavens Divide, from Metal Gear Solid: Peace Walker
Heavens Divide is all about the context. Unlike Snake Eater, you don't hear it right away. You hear it toward the very end, and it comes in at the perfect moment.
Koi No Yokushiryoku, from Metal Gear Solid: Peace Walker
If you plan to play Peace Walker, DO NOT listen to this. This song is the final boss theme.
Encounter, from Metal Gear Solid
Yell Dead Cell, from Metal Gear Solid 2: Sons of Liberty
Rooftop Run, from Sonic Generations
City Escape, from Sonic Generations
Sonic Boom, from Sonic CD
Planet Wisp act one, from Sonic Colours
Super Sonic Racing, from Sonic R
Secret Course, from Super Mario Sunshine
Fever theme, from Dr. Mario (Super Smash Bros. Melee version)
The DK Rap, from Donkey Kong 64
Blast Away! ONE, TWO, and THREE, from Kingdom Hearts
The genius here is the presentation. The first has a light tone, the second has a more brave/heroic-sounding tone, and the third is dark and imposing. Each theme is perfect for when it's used.
Now, let's talk about the series with the BEST music. This series uses its music and its sound effects in a brilliant way, leaving a lasting impression.
The series I'm talking about is Ace Attorney.
Announcing the Truth
The save jingle
And, of course, the most important of all:
This fucking song. This song makes you feel fucking alive. Shit has gotten real, and it's up to you to keep it that way. A dramatic shift is either about to occur, or has just occurred. No one's got shit on you when this plays.