More prophecy than proverb but,

"Technology to wipe out truth is now available. Not everybody can afford it but it's available. When the cost comes down, look out!"

Bob Dylan

I've heard one along similar lines often in my family, but for some reason not in wider use.

"Mitä isompi vika, sitä isompi leka."
(The bigger the problem, the bigger the sledge hammer."

In for a penny, in for a pound

Don't cross your bridges before you get to them

Never date a beautiful woman, only date homely women.

For a beautiful woman may leave you for another man.

So may a homely woman, but who cares, she's homely. :D

A lie well stuck to is as good as the truth.

Light travels faster than sound...which is why most people appear brilliant until you hear them.

It ain't over 'till it's over

Real knowledge is to know the extent of ones ignorance.

Practice makes perfect, but nobody's perfect, so why practice?

Look before you leap

If you think education is expensive, try ignorance.

I have my own proverb

Better to burp and taste it, than fart and waste it.