A voucher for a home improvement shop would come in useful, I should think. They're bound to need some paint or picture hooks or even something bigger. Or for a garden centre, but when people move house they don't usually start by sprucing up the garden.
Or something I like to give newly-weds who I don't know all that well: a voucher for flowers to be redeemed at a later date. Depending on how much you want to spend, you can get a subscription so that they get fresh flowers every month for a certain amount of time.