RSE - Route 113 - Idk why I love this so much. It feels rather melancholic.
Colosseum - Cipher Peon Battle - Also plays during Round 2 of most Colosseum battles. One of the more tolerable tunes in the game. Strangely enough, this also plays in XD but only in Colosseums.
Platinum - Battle Factory - OMG the beats. It feels like the background beat to a freestyle rap or something, I just really like the sounds (base?). The HGSS version is inferior IMO it lacks the 'booms' that Plat does really well.