From Rin's first appearance in ISC (season 1), we have the badass "Bring On Fuzz" by Reinhold Hoffmann. Early on in ES, it was heard again... this time for one of Sousuke'sscenes. For the ES addition it seems to have been renamed "Aggressive Groove".
Beginning Beat from Eternal Summer is a good track to listen to for getting pumped.
Asu e no Last Race, one of Sousuke's only two character songs and probably the saddest of any Free! songs. If Yoshimasa Hosoya's beautiful vocals dont make you cry, the lyrics (in the comment by JoJiJoJo) will.
NEO BLUE BREATHING, featuring Makoto, Haruka, and Rin, is badass yet emotionally cathartic.