There have been two presidential elections decided by the House. Adams vs Jefferson (1800), and Adams (fils) vs Jackson (1824).
But the most contentious of all (until now?) was Hayes vs Tilden (1876). Instead of being decided by the House, the Compromise of 1877 awarded all 20 electoral votes to Hayes, in return for the Democrats' agreement to accept Hayes as President. The Republicans in turn agreed to withdraw Federal troops ending Reconstruction of the South, which enabled the South to proceed to disenfranchise black voters immediately.