We have just been to a wedding where they set up a list of what they wanted. One was a plasma TV so they asked for money towards that. They also had a few gifts and a couple of expensive gifts where you could give X amount. We bought a gift.
We have another wedding early next year and they have asked for money to buy a dining set and have said they will remember the guests this way. As they are from another state and are flying in this makes sense rather than pay excessive baggage.
Normally I prefer to buy a present even if its a voucher, eg, Bunnings