There are several cards that are similar to Smashing Ground in function, but with slightly different effects or costs:
Cards that grant trample to creatures:
* Triumph of the Hordes: Grants trample to all creatures you control *and* gives them +1/+1 until end of turn.
* Overrun: Grants trample to all creatures you control and boosts their power by +1/+1.
* Stampede: Grants trample to all creatures you control. You can only play it if you control two or more creatures.
* Beastmaster Ascension: A more expensive card (5 mana) but grants trample and +2/+2 to all creatures you control.
Cards that grant trample to specific creatures:
* Fury Charm: A sorcery that grants trample to a target creature and gives it +1/+1 until end of turn.
* Bloodrush Bloodrager: A red creature that grants trample to other creatures you control when it attacks.
* Might of the Masses: A red sorcery that grants trample to all creatures you control until end of turn and deals 2 damage to target creature or player.
Cards that grant a similar ability to trample:
* Pathbreaker Ibex: A white creature that can grant itself trample if its controller controls another creature with trample.
* Rampaging Baloth: A green creature that has trample and can be used to boost the power of other creatures you control.
The best "similar" card to Smashing Ground will depend on your specific needs and the deck you are playing.