As a couple in our late 20s who have been living together for more than a year, my fiancé and I have all our household necessities and are not inclined to set up a conventional registry. What we could really use is money for a down payment on a house.  Is there a tactful way to get the word out that we'd prefer cash?

The tried-and-true method of telling people what you'd like is word of mouth.  It's a good idea for couples to provide their parents, their attendants and those close to them with a list of registry sources or, as in your case, let them know cash is preferable.  But remember that there's no dictating to guests what they must give; it's their prerogative to choose.  If you're asked directly, be honest and polite: Say, "We're saving for a down payment on a house, so if you'd like to give a check, that's how we'll use it.  But whatever you decide will be terrific.  Thank you for thinking of us."  Cash presents are perfectly acceptable - as long as the guests feel comfortable with the idea.  Some people just don't like giving money, and that's OK.  For this reason it's a good idea to set up a traditional registry too - even if it has only a few items on it - so guests have a sense of what you like and need.

Here are some suggestions for other new-age traditions.