There are a million places online you can download every midi or CD soundtrack for every single Pokemon game so I'm going to focus on my favorite Pokemon songs here. I hope you download a few and that listening to them makes your day a little better.
Tokiwa Forest (Viridian Forest)
Show Me Around
Tamamushi Game Corner
Silent Hills (Spaceworld Beta, MP3)
Village Bridge (MP3)
Kagome Town (Lacunosa Town, MP3)