We've heard of an interesting product, called SuperView, in the works from SuperMac's wizards. They've come up with a video adapter for the PowerBooks that connects a PowerBook to almost anything that can display a picture short of a Nintendo GameBoy. The adapter is housed in an external case with a built-in, international AC-input power supply, and it connects to the PowerBook via the external SCSI port.
SuperView will have three output jacks, a standard Mac DB-15 RGB connector for normal Macintosh monitors, a standard VGA connector for PC monitors, and most interestingly, an RCA connector with composite NTSC (we're talking basic TV here) or PAL (European basic TV) for the European version. The RCA jack will be suitable for use with a VCR, projection TV, hotel TV, etc., as long as the TV or VCR uses a Video-In RCA jack for input, but it won't work with those icky RF modulator boxes from Radio Shack that never provide a decent picture.
Thinking back to our Pong days, we wondered if SuperView could provide acceptable picture quality on TV sets. Apparently SuperMac is working on some software that will attempt to compensate for the limited picture quality. This limitation goes back to the fact that TV sets draw interlaced pictures, so the electron gun draws every other line, then goes back and draws the missing lines. Since we all listened to our mothers as children and don't sit too close to the TV screen, we seldom notice the interlacing. In rigorous computer use, though, it would be eye-achingly obvious. Apparently some presentation graphics programs also know how to adjust images for the best appearance on NTSC or PAL, which will also help the quality a bit.
Even with SuperMac's tweaking, we doubt that you'd want to use a TV as a monitor for long. That's not the point, though, because SuperView supports all standard Mac and VGA monitor resolutions up to 1024 x 768 at up to 75 Hz (fast and flicker-free) refresh rates. You can drive any monitor in 1-bit (monochrome) or 8-bit color mode, with the exception of the Apple 15" Portrait Display, which apparently has some technical quirks that limit it to 1-bit mode with SuperView.
There are two main ways to use a second monitor on a computer. The Mac generally uses the extended desktop mode, which seriously increases productivity by giving you both monitors to use at once (both screens are active and you simply drag the mouse between them). The second method, presentation mode, duplicates the picture on both screens, which is useless for normal work (unless you have two heads) but ideal for presentations, in which you want to see the projected image on both screens. Initially, SuperView will only support the extended desktop display mode, but presentation mode will come along a little later.
It's too early to guess at prices or shipping dates, but if you travel frequently with your PowerBook, SuperView might be well worth looking into for expanding your display horizons.