penny for your thoughts

a pound to a penny

Very likely; almost certainly.

bad penny

A person or thing which is unpleasant, disreputable, or otherwise unwanted, especially one which repeatedly appears at inopportune times.

collect one's thoughts

To become mentally composed, especially after being distressed, surprised, or disoriented; to become calm or organized in one's emotional state or thinking, as in preparation for a conversation, speech, decision, etc.

have second thoughts

To change one's opinion, or be uneasy about a previous decision.

not leave one's thoughts

To remain in one's mind for a long duration.

penny in the fusebox

An improvised repair made with no regard for safety.

penny pincher

One who spends little money; one who is very frugal or cautious with money.

penny wedding

A wedding at which the guests contribute payments in order to fund the event and to benefit the newly-married couple.