İpsala-Kipi border crossing
It's not allowed to cross border by foot, but as there's lot of trafic, finding a ride would not be a problem.
While crossing the border from the Greek side, policeman on checkpoint will give you stamp in your passport even if you don't have a ride, which makes finding a ride much more easier. You can try it after the duty free shop at petrol station where trucks usually refill their fuel. And one very nice fact: drinks from coffee machine at that petrol station are free :)