Here is the music in Donkey Kong Land: http://www.youtube.com/watch?v=iS6jMnYUrx4&fmt=18
And here it is in Blast Corps: http://www.youtube.com/watch?v=qWmtVAm16-M&fmt=18
Hear the resemblance? It's not too surprising, though, as Graeme Norgate supposedly worked on the music in both games.
I can think of a few more examples related to the Banjo games as well. In Banjo-Kazooie, there was some fanfare music that you can hear if you get the secret eggs. This music was then reused in Donkey Kong 64 before fighting a boss. Another example was in Banjo-Tooie in a scene near the end of the game where a short part of the music was taken from K. Lumsy's theme in DK64. If you want to know exactly where you can hear this, then read below...
Spoiler!
One last one is yet another Banjo one. In a BK trailer, you can hear a peculiar theme at the last 7 seconds in Clanker's Cavern. This song was never used in Banjo-Kazooie, but was used in Fungi Forest in DK64! Also, I think this may be related to the fact that there was a level planned in Banjo-Kazooie called Fungus Forest, but was scrapped and used in Donkey Kong 64 as Fungi Forest instead.
Another game that heavily reused music was the GBC version of Donkey Kong Country. About half the songs were taken straight from Donkey Kong Land, even those that weren't originally from the SNES version (like the cave, temple, underwater ruins, and even the title screen music). And there was one ripped straight from DKL3 as well: the music when you fail a bonus stage.
Know of any other reused music?