I prefer personal messages too. I know some people think that any card is better than nothing, but I feel people deserved to be thanked properly for their thought and consideration.
When I was looking for something to write in the cards, I came across this for cash gifts "Thank you for your *generous/thoughtful gift. We really appreciate it as we start our new life together".
*You can add words like "very" or "extremely" etc depending on how much they gave (which I find somewhat distasteful myself, so I used "extremely" a lot!)