It has been said more than once, but we have to start placing camera's on the goal line immediately to review if the ball has crossed the goal line after questionable goals. The assistant referee simply can't judge this from big distances or if he is not in parallel with the goal line. Too much is at stake!
Already a lot of games where teams have won although the goal they scored was clearly over the goal line after video review.
For example the England vs Ukraine match on Euro 2012 on June 20th 2012 where England scored a goal that was clearly well over the goal line.