寿终正寝
die in one's bed
Her father died in his bed last night.
　
对牛弹琴
cast pearls before swine
The old professor felt that lecturing on semiotics to undergraduates would be casting pearls before swine.
　
截然不同
(as) different as chalk and cheese
I don't have anything in common with my brother. We're different as chalk and cheese.
　
维妙维肖；栩栩如生
to the life
John can copy his teacher's manner of speaking to the life.
　
精打细算；省吃俭用
scrimp and save
For years we had to scrimp and save, but now we can enjoy life more.
　
精疲力竭
flat out
He was flat out after his night's work.
　
说曹操，曹操就到
speak of the devil
Why, speak of the devil -- there's Amy.

附注：这成语是从 "Speak of the devil and he's sure to appear." 缩略而来。

需要乃发明之母
Necessity is the mother of invention
The first prisoner to tie together bedsheets to escape knew that necessity was the mother of invention.

养尊处优
live off the fat of the land
The tiny upper class lived off the fat of the land while many of the poor were starving.

种瓜得瓜，种豆得豆
As you sow so shall you reap
As you sow so shall you reap. I'm a firm believer that we create our destiny.

竭尽全力；全力以赴
do one's level best; with (all one's) might and main
I was convinced that he did his level best to find a new girlfriend.
She pulled on the rope with all her might and main.

附注："with might and main" 这成语算是累赘，因为 might 和 main (名词) 都意为「力量」(strength or power)。

铢两悉称；半斤八两；不相上下
six of one and half a dozen of the other
I say she's a stewardess. She says she's a flight attendant. It's six of one and a half dozen of the other.