In Brussels, La Papeterie Anglaise has a long tradition with printing all the documents that you need, whether you like them traditional or modern. Plus, they have really beautiful greeting cards from international brands like Kate Spade. Paperland also prints your invitations in the best quality.
In the US, wedding cards can be fabulous: Nothing can match the luxury couture invitations of Ceci New York, but Minted and Wedding Paper Divas are definitely great online destinations to make your selection!
Once the wedding invitations have been sent, you can always open an account with Wedding Windows, which provides a beautiful and useful information tool for your guests.
I'll share more European addresses with you in a while.