A first grade teacher collected old, well known proverbs. She gave each kid in her class the first half of a proverb, and had them come up with the rest.
These are great:

• As You Shall Make Your Bed So Shall You... Mess It Up.
• Better Be Safe Than... Punch A 5th Grader.
• Strike While The... Bug Is Close.
• It's Always Darkest Before... Daylight Savings Time.
• Never Under Estimate The Power Of... Termites.
• You Can Lead A Horse To Water But.. How?
• Don't Bite The Hand That... Looks Dirty.
• No News Is... Impossible.
• A Miss Is As Good As A... Mr.
• You Can't Teach An Old Dog New... Math.
• If You Lie Down With The Dogs, You'll... Stink In The Morning.
• Love All, Trust.. Me
• The Pen Is Mightier Than The... Pigs.
• An Idle Mind Is... The Best Way To Relax.
• Where There's Smoke, There's... Pollution.
• Happy The Bride Who... Gets All The Presents!
• A Penny Saved Is... Not Much.
• Two's Company, Three's... The Musketeers.
• Don't Put Off Tomorrow What... You Put On To Go To Bed.
• Laugh And The Whole World Laughs With You, Cry And... You Have To Blow Your Nose.
• Children Should Be Seen And Not... Spanked Or Grounded.
• If At First You Don't Succeed... Get New Batteries.
• You Get Out Of Something What You... See Pictured On The Box.
• When The Blind Leadeth The Blind... Get Out Of The Way.