Home remodeling has become one of the great American pastimes -- $127 billion spent in 2004, and $150 billion more in 2005, according to Harvard's Joint Center for Housing Studies.

And there's no letup in sight.

Kermit Baker, director of the center, says that a "significant core" of the population spends more than 50 percent of their homes' value on remodeling and improving -- some solely to enjoy the updated space, others for investment, hoping the outlay will pay big dividends when they sell.

Which rooms are they spending it on? Here are some of the most popular items in home improvement today:

Kitchens
Kitchens, perhaps even more than living rooms, are becoming gathering spaces. People want the design of the room to reflect that, says Bill Golden, a Realtor at RE/MAX in Greater Atlanta. Homeowners are taking down walls that separate kitchens from dining rooms and living rooms to create a more casual, open feel.

Doing away with Formica countertops, homeowners are looking at more attractive, durable and expensive options including quartz and granite counters.

"People are adding islands and [upgrading] finishes," says Golden. "A big priority is stainless-steel appliances. Hardwood floors are also popular."

Outdoor rooms
Whether it's a three-season porch or a patio, more people are trying to make the space outside their house as comfortable as the rooms inside it, according to television personality Kathy Peterson, author of "Great Outdoor Decorating Makeovers." Spaces with sinks and barbecue pits, gas stoves, and refrigerators are increasingly popular.

"People have realized that they've been neglecting their outdoor spaces," says Peterson. "They're making outdoor spaces an extension of their home by bringing the inside out." Not only is the space more casual than a formal dining room, it's a great way to entertain, she says.

Master bathrooms
Golden says he's seeing a movement toward large, luxurious showers with multiple shower heads and glass enclosures -- replacing, in some ways, the large whirlpool tubs more common in years past. There is also a growing interest in mosaics. In colder climates, in-floor heating and heated towel racks are gaining popularity, as well.

Perhaps most striking is the move toward ever-larger bathrooms. Gone are the tiny spaces of the past, where a toilet and shower-and-tub combo were wedged into 20 square feet. Today, homeowners favor spaces that can accommodate a separate shower and tub, double sinks, and ample storage.

Home offices
No longer relegated to a musty corner of the basement, home offices are bigger and brighter than they used to be. Thanks to trends like telecommuting and the ever-increasing demands of the office, people want to be able to work in comfort.

In addition to creating spaces with lots of light and windows, homeowners want to make sure to have plenty of space for desks and file cabinets and want include plenty of power outlets for electronics, as well as wiring for Internet connections, phones and fax machines.

Closets
New closets are designed to be spacious, organized and well-lit. While one walk-in closet used to suffice for the master bedroom, some couples are now looking for two separate closets. The closets often include custom shelving, clothing rods, pegboards, mirrors and even seating. Popular surfaces include wood veneers and wood with glass insets.

As these new styles have surfaced, other common renovations have fallen to the wayside. You'll find fewer people adding an extra bedroom in the basement or garage, for instance. Overall, trends focus on opening up and enlarging spaces, improving finishes, and making spaces casual and comfortable.

Ready to remodel? Get ideas for your home improvement project.