Mega- Piranha

The group the mega- piranha's belong to is #23.

Deliver Us From Evil

"This is someone we've known for 23 years."

There are a few more, but it is a touchy subject so I won't include them.

The Butcher

There are several 23's in timestamps throughout.

Daybreakers

Ethan Hawke's brother's jacket says 23 on the sleeve. I don't remember his name.

Broken Flowers

During the opening credits, one of the post office machines is tagged A-23.