The Pokémon DP Sound Library lets you listen and use the Pokémon Diamond & Pearl Soundtrack
If you want to listen to the music (and sound effects) from just Pokémon Diamond and Pearl, you can now do so in a legally sanctioned way by this new website from The Pokemon Company. The Pokemon DP Sound Library is now available for most of the world and features the entire soundtrack from Pokemon Diamond and Pearl.
On the website, you can listen to all the music from the game, download it and even use it in your own personal (non-commercial) projects. There are also different playlists for different moods.
Now, if we could get music from other Pokemon and Nintendo games as widely accessible…
There’s also this hours long video featuring it all if that’s more up your alley.