I have two that I tend to use often =D

猿も木から落ちる。
(さるもきからおちる)
Even monkeys fall from trees. (ie – nobody is perfect)

嘘つきは泥棒の始まり。
(うそつきはどろぼうのはじまり。)
A liar is a beginning of a thief. (ie – don’t lie, it’s a slippery slope) ;)