Additional options would be Rob the Archives , Jeska's Will , Commune with Lava , Act on Impulse , and Reckless Impulse
Of the Zendikar creature-lands, Celestial Colonnade and Creeping Tar Pit are obviously the best, as they can give you an evasive beater to get those last points of damage through
Though technically an IR and not a SIR, its value speaks to the strength of its artwork and the bond it shares with its twin
Twinflame Tyrant, Herald of Eternal Dawn, and Bloodthirsty Conqueror Fracture Foils are also in the $200 range
Gladiolus Amicitia By the time you put Gladiolus Amicitia into play it's less about ramp and more about how to measure your landfall triggers to get the most out of them, and granting +2/+2 is the perfect complement to trample
In terms of mechanics, before a game of Commander starts, each player sets aside their commander before shuffling their deck