It would be better to put something personal in it, but seeing as you're stuck for ideas, I plucked these from a site- they're a bit twee, but you might be able to adapt one or two of them.
Love and best wishes on this very special occasion.
"Today is a day you will always remember. The greatest in anyone's life.
You'll start the day just two people in love and end as husband and wife."
Wishing you a love that grows day after day and year after year. Congratulations on your Wedding/Engagement
Your engagement/marriage is a special moment in time... a day to look towards the future and all it holds... and a day to wish you all the happiness in the world.
Congratulations. Wishing the both of you all the happiness in the world.
Congratulations and warm wishes to both of you on your wedding day.
Congratulations and the best to you always.
Wishing you a world of happiness for you.
A day to wish you all the happiness in the world