Gangplank Galleon starts out sounding like a merry sea chanty played on a squeeze box, only to become dark and ominous (complete with a shift from a bright major key to a gloomy minor key) after a few seconds as the final boss fight against King K. Rool stops being mere child's play.
DK Island Swing, the first level music, is two awesome tracks for the price of one, the first bright and energetic to get the player fired up for the fun ahead, the second eerie and atmospheric (and, in the first level, Jungle Hijinks, often kicking in just as the sky clouds over), and both of them providing some of the series' more familiar Recurring Riffs.
Welcome to Crocodile Isle. A spooky and threatening track that plays in the awesome Donkey Kong Country 2 as you enter the Kremlings island to rescue Donkey Kong.
And the GB version of the above from Donkey Kong Land 2. Not quite subtle, but still pretty epic.
Stickerbush Symphony, a trance-like soothing techno track that is often voted one of the best video game songs of all time.
Of course, if you hate the Stickerbush levels with a passion that borders on sociopathic obsession, then Stickerbush Symphony is enough to send you into fits of rage at the memories of dying over 30 times. Others may find the music being the only thing keeping them from breaking their controllers and TVs on those stages due to how calm, mellow, and soothing the track is due to it playing on such difficult types of stages.
Sadly, "Disco Train" is pretty much always drowned out in-game by the fireworks and rail screech effects in the levels where it's played, to the point that the kick-assery of the tune can only be appreciated via the OST.
There's also the rockin' Monkey Mountain theme, which goes high and low and all over. Dah dah dahdahdah, deerrr ner ner ner...
For more awesome original tracks created specifically for new types of level Archetypes exclusive to the first Donkey Kong Land, there is the music for the Cloud Levels, showing that the first Donkey Kong Land can stand on its own in greatness, both in its originality department in its new type of levels as well as its own original music, and showing that it's not just some watered down port of the first SNES game in the series with weak 8-bit music tracks from DKC 1.
The 8-bit remix of 3's"Enchanted Riverbank." It puts more emphasis on the melody, and really lets it shine through.
The chiptune version of Lockjaw's Saga somehow manages to sound as epic as the SNES version.
The Boss music is pure, gratuitous awesome. Think of all the rock bands which just can't approach this kind of catchy.
The Donkey Kong Land 2 version of Donkey Kong Rescued arguably surpasses its 16-bit counterpart.
Another great 16-bit to 8-bit conversion in the second Donkey Kong Land is its version of Stickerbrush Symphony. For as hard a time Grant Kirkhope had creating this soundtrack (the first video game he ever composed for) - he has admitted he nearly quit (thankfully he didn't) - he did an awesome job considering the limited hardware he had to work with.
Donkey Kong Land's Temple Theme. Very different from its counterpart and just as good.
Trivia: "Jungle Japes" as a title has by and large supplanted "DK Island Swing" as the title of the song. This version of the music is especially fun due to the song having layers of Banjo-Kazooie awesome.
The Boss Remix belongs to one Army Dillo, who was also the Crystal Caverns boss after some cybernetic enhancement.
Even though Kenji Yamamoto of the Metroid Prime series is the new composer and there are mostly remixes, that doesn't make the music any less awesome. One such theme is Mine Menace/The Rocket-Barrel stages.
Special mention should go to the remixes of Northern Hemisphere and Life in the Mines, for their effective remixing to fit their new settings: a desolate cliff side and factory basement, respectively.
Tidal Terror (which is another remix of Northern Hemispheres). You can really hear the influence of Metroid Prime here.
Although each and every mine cart stage contains its own unique cover of "Mine Cart Madness" from the original DKC, "Rickety Rails" is the only one to feature an entirely new arrangement of the piece. And IT. IS.AWESOME.