"No Helping It!!", an instrumental version that's ridiculously epic, even out of context. Aside from the opening theme, this the very first piece of music we hear in the series, and it accompanies the Action Prologue. It's also the fanfare they use for the brief recaps that start most of the episodes.
It also holds a special meaning to many Fraxy players.
"Is It Okay To Just Get Fired Up?", the villain's victory song usually, music played when the enemy's really starting to get a solid advantage and you wonder the outcome. Not like you should, but... y'know.
"Spinning, Spinning, Spinning, Spiii!?" was good, but normal background music until Lagann-hen, at which point it becomes the theme for creating Chouginga Gurren Lagann, Simon AND his mech obliterating everything and crying manly tears of blood, and the Dai-Gurren-dan going on an utter rampage in the name of vengeance and lost brothers.
There are two versions of "Sorairo Days" appended with Tengen Toppa EDITION. If it also has Lagann EDIT then it's from the movie, the other one splices the tune of "Tsuzuku Sekai", "Happily Ever After" and a third song into it for an interesting but not quite as dramatic form of awesome. Can be heard here.
Also from the second movie: "My XXX is the Best in the Universe". In the same vein as the famous "Row Row Fight the Power", but with brand new lyrics and a beat that will pierce the heavens.