Bubble Bobble (NES)
They may have lost the original arcade source code somewhere along the way, but that certainly never stopped Taito from trying to port it to anything with a CPU.
Track 35 on the NSF (34 in the sound test) is an interesting folk dance-like tune, normally accessible through the sound test. This tune is not in the arcade version, so it was probably included as a bonus for those who managed to unlock the sound test.
Interestingly, this track was used in the American/Japanese version of Rainbow Islands as the staff roll theme!
There are still a few more differences.
The NES version has a new Taito logo. The FDS version is identical to the one seen in the original arcade version. The Bubble Bobble logo was also moved to make more room for the new "licensed by Nintendo of America Inc." text.
The FDS version uses the save function to select the current level progress. The NES version allows the use of a password system to select levels.
The intro text was given a clean up for the NES version. For some reason, the exclamation mark was made taller.
For some reason, the FDS version leaves the PPU's red emphasis bit on at all times, giving the entire game a red tint. The NES version leaves all emphasis bits turned off.
In the FDS version, return to the game selection screen immediately after the music is played. The password is added in the NES version, After the music is played, the player needs to press the start button to return to the game selection screen.