That SNES version of DKC aquatic ambiance (underwater level) is still somewhat popular, but I also think this GB/GBC version is a good reinterpretation:
Not exactly a chiptune (it was on the Wii) but I found this track randomly when hunting for something else and for a fucking Yugi-oh game, it goes pretty hard.
My go-to for bumpin' chiptunes is always NES-era Sunsoft shit (at least for stuff that not everyone's heard a million times).
OCEAN loader music. In the mid-80s, some clever coders found out that it's possible to play SID music while loading a tape game on C64. OCEAN had four or five of those loader music pieces and they became legendary among fans. I liked the first one here a lot, that and the great loader graphics really tuned you in for the game that was to follow (Arkanoid in this case) and made waiting for it to load a little more pleasant. So pleasant in fact that I sometimes loaded a OCEAN game just to listen to the loader music.