Nothing at All
A gift should always be sent as a thoughtful gesture to the bride and groom -- even if the giver can't attend the wedding.
Deciding how much money to spend on a wedding gift can be difficult, but a good rule of thumb is to buy a gift in a price range that reflects how well you know the couple. If you consider the bride and groom to be close, personal friends, you might be inclined to buy them a more expensive wedding gift compared to another couple that you only see or talk to once a year.
Wedding gift etiquette says that it's appropriate to send a wedding gift up to one year after the couple says "I do," but this is a bad idea for many reasons. A year later, the couple's registry might be completed or even deleted. Besides, the bride and groom have probably moved on from appliances and fine china and need other household items like window treatments, yard tools and furniture. It's a little awkward to ask the couple what they need a year after their wedding, and more than likely, they'll feel just as uncomfortable telling you what they would like to have.
Waiting months after the wedding to give a couple a gift increases the likelihood that you'll forget about buying them a present altogether. At least send the couple a card right after the wedding, and get around to the gifting when you can.