They're not just for traveling anymore. Notebook computers are becoming the tool of choice for business users, wherever they happen to be working. The research firm Gartner predicts that by 2009, more than half of all PCs sold will be portables, and small-business buyers--who crave on-the-go flexibility for themselves and their employees--are leading the charge, says Gartner analyst Leslie Fiering. These days, it's easy to find business-ready laptops from big manufacturers for less than $600. But for those who want something more specialized and powerful, there's a slew of new choices. Here are six that stand out.

Best for… Taking abuse

What it is: A nearly indestructible notebook that meets U.S. military standards.

What's cool: It can survive 26 drops from three feet, as well as extreme high and low temperatures, rainstorms, and other hazards of mobile computing. It weighs only 6.8 pounds, which is quite light for a fully ruggedized notebook. It has a built-in global positioning system.

Drawbacks: Even though the GoBook is larger than the typical laptop--11.8 by 9.65 inches--its display is a relatively small 12.1 inches and can be difficult to read in sunlight. The GoBook will not support Windows Vista (NASDAQ:MSFT) until the end of 2007.

Price: Starts at $4,195.

Best for… Working while the computer's off

What it is: A notebook computer with two screens--a standard display and another 2.8-inch screen on the outside of the case.

What's cool: That secondary screen can be set to show whatever data you want, even when the computer is turned off--a useful tool for checking your calendar and e-mail. It comes with a built-in Web camera and weighs less than four pounds.

Drawbacks: The second display gives the computer a small hump, making it bulkier than other notebooks. Plus, an extra screen doubles your odds of having a technology breakdown (though the computer comes with a two-year limited warranty).

Price: $2,199 for a machine with 1.5GB RAM and a 160GB hard drive.

Best for… Traveling really light

What it is: A one-pound portable computer that runs Windows.

What's cool: Despite its small size, the OQO has features that match mainstream Windows notebooks, including a hard drive of up to 60 gigabytes, a 1.5-gigahertz processor, and built-in Wi-Fi. You can get it installed with an optional cellular modem as well. The casing is made of magnesium alloy, which will help protect the computer if you drop it.

Drawbacks: The display is only five inches across, and even though the OQO is bigger than a BlackBerry (NASDAQ:RIMM), you'll still have to type with your thumbs. The display also lacks the high resolution typical of bigger laptop displays. And there's a four- to 10-week waiting list to get one.

Price: $1,499 to $1,849, depending on configuration.

Best for… Making presentations

What it is: A stylish notebook that integrates various kinds of presentation software and hardware.

What's cool: It comes with a remote control and easily connects to most projectors. Each machine is loaded with Apple's Front Row content-creation software, which makes it easy to organize video, audio, and photographs. Also standard is iSight, a camera and videoconferencing tool. And now that the MacBook uses Intel processors and can run Windows software, longtime PC users may want to give it a look.

Drawbacks: The MacBook Pro is a lot more expensive than a comparable Windows laptop. Some Windows software runs more slowly on the Mac than on a PC.

Price: Models with a 17-inch screen start at $2,799; models with a 15-inch screen start at $1,999.

Best for… Taking your desktop with you

What it is: A desktop computer crammed into a laptop casing, with a 20.1-inch screen (bigger than many desktop monitors) and two hard drives with nearly 320 gigabytes of storage.

What's cool: The Envy is designed with hard-core computer gamers in mind but can be useful for anyone with heavy graphics or data-crunching needs. It features high-end graphics and a theater-style audio system. And it's finished with high-gloss auto paint.

Drawbacks: It's big. This thing measures 18.75 by 13.5 inches and weighs 16 pounds. Battery life is just 30 to 45 minutes.

Price: Starts at $4,900.

Best for… Doing double duty

What it is: A conventional notebook that, with a swivel of the screen, converts into a touch-sensitive tablet computer that works with a stylus--a useful tool for tasks like filling out forms.

What's cool: The Portégé comes with a built-in biometric password device--it recognizes your fingerprint--so that even if your notebook is stolen, your data will be safe. In its basic configuration, it weighs less than four pounds, making it easy to travel with. Both Wi-Fi and a Verizon (NYSE:VZ) cellular modem are built in.

Drawbacks: The display is just over 12 inches, a relatively small screen for a notebook. The price is high compared with that of a basic notebook.

Price: $2,599 to $3,499, depending on configuration.