After Suzy Ellis and her boyfriend got engaged, they considered several Southern California locations for the wedding, including upscale hotels such as the Ritz-Carlton Laguna Niguel and the Biltmore Santa Barbara. But nothing was quite what they had in mind.

“Whenever we looked at hotels, people would be standing on their balconies, gazing down at the wedding site,” says the 26-year-old Dallas resident, who handles P.R. and marketing for a fashion company. “The thought of strangers being privy to what was going on seemed so wrong. I wanted my wedding to be a private, intimate occasion.”

So Ellis chose Villa Casa Bella, a bluff-top coastal estate in Santa Barbara, California, that comfortably sleeps 20 guests and can host parties of up to 250. The bride-to-be arranged to rent the property, which is the primary residence of a local family, which relocated to its second home nearby while the festivities were under way. Ellis and her family stayed at Villa Casa Bella, hosting five days of events, including a Mexican-fiesta-themed rehearsal dinner, a spa party for the bridesmaids, and a Saturday-afternoon reception for 150.

From Cape Cod to California, spectacular estates, mansions, and villas are becoming available, for a price. They aren’t museums, catering halls, or city properties, but private homes—in many cases, belonging to owners with several residences.

“A real estate investor may have homes throughout the U.S.; he can’t live in them all at the same time,” says Dan Caporale, general manager at Carefree Lifestyle, a Miami company specializing in luxury rentals nationwide. “Rather than having the house just sit there, they can get some good use out of it. They’re smart, successful businessmen; they see a return on their investment.”

Aaron Kreye, whose family owns the Arcus Estate, a two-house waterfront property on Martha’s Vineyard, agrees. “There’s extra money you can make, and the property’s just sitting there, so why not?”

Even though some properties must be rented for a week and others require a five-figure security deposit, as more and more couples seek to personalize their lavish weddings, estates like Villa Casa Bella are becoming increasingly popular venues.

“Estate weddings are the No. 1 request that I get,” says Kimberly Pilson, a wedding coordinator who runs HamptonsWeddings.com, an online resource for those planning nuptials. “I’ve received more and more requests over the past three years. People are tired of traditional banquet halls or hotels.”

The trend is fueled, in part, by the children of affluent baby boomers, who are coming of age and tying the knot, wedding experts say. Backed by immense parental wealth, the young and ready-to-wed are opting for increasingly lavish weddings—the average cost of a nuptial event nearly doubled from 1990 to 2006, according to Condé Nast Bridal Group, which is owned by the parent company of Condé Nast Portfolio.

Finally, all couples want their wedding to be “different,” whether it’s the location, the dress, or the reception-dinner favors that set it apart.

It’s not just about making money for the homeowners; some owners of luxury homes simply enjoy contributing to someone else’s happiness. The Baker Estate—a seven-bedroom waterfront home on just over four acres in Hampton Bays, New York, that rents for about $20,000 a month—typically hosts two weddings a year, in May and September.

Many estates allow weddings only on a case-by-case basis, since the homeowner decides who can use the property for what purpose. “A lot of them have very strict rules about what can be done, what can’t be done,” says Gabrielle Longhi, a wedding coordinator in Maui. For example, there may be a limit on the number of invitees, or guests may be prohibited from using certain areas of the house.

At the Arcus Estate, a one-week rental in the spring or fall costs $2,500, but a five-day wedding rental is $5,000. “It’s not worth it for us unless we charge more,” Kreye explains, noting the extra work involved in making the house wedding-ready, from painting to doing yard work to rerouting electricity so the patio is primed for music and lights.