I love thunderwave, it'll knock the enemy's socks off. If it is on my spell list then I will almost always take fireball at the first opportunity because it's a classic. I also like faerie fire as an option as a bard or druid. fog cloud is another favourite spell.
I've only ever played a cleric once, but I loved being a dextrous elven cleric using spirit guardians in conjunction to my standard attack and spiritual weapon.