Worn Powerstoneramp$0.36Like Sisay's Ring, it is a colorless mana rock that helps jump from four mana into larger spells. It produces immediate mana acceleration, though it enters tapped.
Thran Dynamoramp$3.60A classic colorless accelerator that taps for a large burst of mana, filling the same role as Sisay's Ring in big-mana decks. It is stronger at producing mana, but costs more.
Dreamstone HedronrampBudget$0.19Another four-mana artifact that ramps into higher-cost spells with a colorless mana burst. It also has an alternate card draw mode later in the game.
Hedron Archiveramp$0.25Very similar to Sisay's Ring as a four-mana colorless ramp artifact. It produces two colorless mana and later can be sacrificed for cards.
Coalition Relicramp$0.33A flexible mana rock that provides colorless acceleration and can store mana for future turns. It serves a similar midgame ramp function, with added fixing potential in multicolor decks.
Ur-Golem's Eyeramp$0.35This is one of the closest simple analogs: a four-mana artifact that taps for two colorless mana. It is the most direct functional comparison to Sisay's Ring.
Firemind Vesselramp$0.31A colorless four-mana rock that ramps by two, closely matching the rate of Sisay's Ring. It is weaker in speed because it enters tapped.
Everflowing ChalicerampBudget$0.19A scalable artifact mana source that can fill the same role as a colorless ramp piece. It is more flexible, though its output depends on how much mana you invest.