The cards I mentioned above are more or less the only ones that I rent.

Some useful cards (less 1DEC/DAY/CARD):

Neutral: Creeping ooze, Goblin mech, Sand worm
Green: Nectar queen
Blue: Sea monster, Venari Wavesmith
White: Djinn Renova, Lorna Shine, Baby Unicorn
Red: Fineas Rage, Lava Launcher
Black: Owster Rotwell
Dragon: Djinn Chwala

I don't play Dragon/Green if i can.

The more important is to play the rule and counter the opponent. For exemple, Owster Rotwell can win a game by himself if you know the opponent will play magic.

After that i only rent for power, it can be long the first time to check for cost effective cards but after that just don't forget to renew the rent.