Can you ask for money on your invitation?
This is one of the most controversial topics I am asked about and after extensive research, I found that the Canadian Oxford Dictionary has this listed as a Western Canadian tradition! Guess where I live? Western Canada -- Yay!!! Yes, 'tis true, the Prairies ROCK!
How do you word it?
Presentation only
Now, I know you won't believe me and you may want to use the cute poems and whatnot as an insert but as a soon to be married person, keep in mind that it takes all kinds and any way you ask is going to offend someone. The best thing to do is to register for a couple of really big things that you would never be able to afford yourself to promote a "group gift", register for a Honeymoon Registry, or do something like this:
"We have two of everything, our house is all full,
She has the dishes and he has the tools,
But if you feel you must give us something new,
Know that a gift card to these places will do.
List some favourite restaurants, movie theatres, book stores, hardware stores, housewares, etc."
Or:
"No boxed gifts but gift cards and certificates from (List some favourite restaurants, movie theatres, book stores, hardware stores, housewares, etc.) will sure help us out down the road"
Again, don't expect everyone to like it, but those are probably the same people that don't approve of living together before marriage either...
The internet is a great resource too, so feel free to do what you want!