What features should I look for?

Look for color displays that are easy to see in all lighting conditions, such as the one found on the Garmin 276C--considered one of the best-regarded screens in the industry. The larger the display, the more expensive the unit will be, but even big screens can be difficult to read in direct sunlight. Also, check the viewing performance of the display to make sure you can read it from any angle. In this respect, most of the dedicated GPS units outperform PDAs, but at a price.

Look for color displays that are easy to see in all lighting conditions.

Some manufacturers charge extra to unlock maps from their Web sites or CDs, while others include only partial regions or merely main roads. Make sure you get street-level maps. Main roads only are of no real utility. Things can get expensive if you're planning a cross-country trip unless you can make use of free community maps, for example, maps found at Malsingmaps which offer excellent Malaysia and Singapore maps, and links to maps of other countries like Australia.

Maps are largely device-specific. So in making your purchase decision, factor in the cost of the maps you want to use and also the cost of updating them.

Make sure you can update the unit's firmware and mapping data. On most portable models, a USB or serial port lets you connect the system to a PC where you can upload the latest maps and system software as these become available. On in-dash models, maps are typically read from an integrated DVD or CD player and require only the latest discs to be brought up-to-date.

Choose a GPS unit to fit your traveling habits. If you do a lot of long-distance driving in the US or Europe, consider a model with a dedicated hard drive that stores maps of the entire country. Otherwise, just for Singapore and Malaysia, a model that uses an SD card to store maps is a good bet, and you can buy additional cards to load more maps when necessary. If you want to share one unit between many vehicles, look for a model that is lightweight and easy to install and remove from your vehicle. Make sure the rake of your screen can accommodate your GPS with its antenna in its optimal position. For example, the new Honda Civic and Honda Odyssey have very steeply raked windscreens which may not accommodate certain GPS models with their antenna up. Stay away from permanent mounting devices unless you plan on using the unit in just one vehicle.

Like anything else, the more bells and whistles included in your GPS system, the more you'll end up paying. But there are certain features that are more or less standard equipment these days. Street-level maps with voice- and text-prompted driving directions are the foundation of any in-car GPS system worth its salt, and we're starting to see systems that use text-to-speech technology to deliver specific street names rather than more generic instructions, such as "turn right in 0.5 kilometers".

Without text-to-speech, the proper sentence structure of the directions is also important, especially in high-street-density Singapore. For example, it is preferable to hear "in 100 meters, turn left" rather than "turn left in 100 meters" because the latter instruction may just shock you into turning left there and then. This attention to detail separates the good GPS devices from the me-toos.

A comprehensive POI database containing airports, buildings, hospitals, dining options, shopping, service stations, and more is a must if you're traveling in unfamiliar territory, as is automatic routing from a POI, an address book or your present location. Community maps like Malsingmaps have extensive POI because the community keeps on updating it with new finds. Look for a device with touchscreen controls, automatic rerouting when you veer off course, and variable map perspectives such as 3D and bird's-eye views. As you get into the high-end models, look for big daylight-readable screens and compatibility with future real-time traffic and weather alerts which may require an annual subscription fee.

Most in-car navigation systems are ready to use right out of the box and come with everything you need to get up and running in a matter of minutes. Still, there are accessories available that will help you get the most out of your investment, including auxiliary antennas that can be mounted at the base of your windshield to improve signal reception and carry cases to protect your GPS unit when not in use. You can also pick up various mounting devices, including motorcycle-mounting kits and low-profile external antenna mounts that adhere to the trunk of your car. Additionally, you can purchase more maps on CD media or flash memory cards, cigarette lighter socket chargers, as well as AC adapters that let you charge or use your GPS unit at home.

Most companies include the basic accessories such as vehicle mounts and car chargers in the box.