يا واخدة القرد على ماله، يروح المال ويبقَى القرد على حاله

An Egyptian proverb courtesy of Cherine of the wonderful Wordreference forums

يا واخدة القرد على ماله، يروح المال ويبقَى القرد على حاله
Literal Meaning: If you marry a monkey for his money, the money can be lost, but the monkey will still be a monkey.
Meaning: Think twice about marrying an ugly person for his money.

This is my new favorite.