Dialga and Palkia's theme was buckets of win. I loved it so much I just sat there and listened to it when I fought (and easily caught) Dialga.
Other good ones were Cyrus' theme and Snowpoint. Not many in D/P stood out for me...
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"I've seen a lot of things, but this...This is a first."- Ezreal, the Prodigal Explorer, after meeting Rammus