What are some of your favorite or most-used idioms?

[Tarheel]

"Don't count your chickens before they hatch" is a good one.

[Tarheel]

He couldn't see the forest for the trees.

[Tdol]

In BrE, we say that someone couldn't see the wood for the trees.

[Amigos4]

I like "Hold your horses". (Wait a moment)

[Tarheel]

I used this one today (on another thread).

If you can prove me wrong I will eat my hat.

That's just one possible variation, of course.

[Tarheel]

A walk in the park.

[Tarheel]

A piece of cake

[Tarheel]

As easy as pie.

[Tarheel]

Take it in stride.

[Tarheel]

Don't hold your breath

Meaning:

It won't happen anytime soon (if ever).