1. First off, double check the model that you're buying isn't discontinued. For example, Wal-Mart is planning to sell loads of marked-down Garmin c330's. The c330 was a great GPS when it was released 3 years ago, but you buy a better GPS for the same money today. For more details on the c330, check out THIS ARTICLE.
2. Next, make sure the GPS you're considering isn't on the GPSmagazine List of Units to Avoid.
3. Be sure to check out the GPSmagazine Buyer's Guide.
4. When considering which GPS to buy, remember that more features doesn't necessarily equate to a better GPS. Garmin seems to have the best routing engine, followed by Magellan, then TomTom. So if you're primary concern is picking a GPS that will get you from point A to B via the "smartest" route, then I recommend Garmin above the others. To date no other GPS company has been able to match Garmin's routing logic in my tests. Magellan makes good models, although Magellan's customer support is notoriously terrible - something to take into account if you decide to take Amazon up on their $100 pricing for the Maestro 3140.
5. Quick Picks: Based on the current pricing, I'm highly recommending the following models:
   1. Garmin nuvi 650
   2. Garmin nuvi 660
   3. Garmin nuvi 350
   4. Garmin nuvi 200
   5. Magellan Maestro 3100
   6. Magellan Maestro 3140
   7. Check out the Black Friday sales for more recommended deals.
6. Make sure the sale price is actually a sale - many unscrupulous retailers are offering "marked down" sales that are still more expensive than buying the GPS online. Check any in-store pricing with online pricing from reputable e-tailers like Amazon.com.
7. Here are some general guidelines that will help arm you with the right knowledge to find the right GPS tomorrow:

   SiRF – Make sure your new GPS uses SiRF’s high performance receiver (officially called SiRF StarIII). This new chip significantly enhances GPS signal performance, making it possible to get solid reception behind talk buildings, canyons, under tree cover – even indoors! Note that Garmin's newer 200 and 700-series nuvis don't specifically state it, but rest assured they use SiRF (as of this writing).

   NAVTEQ Maps – It goes without saying that one of the most critical elements of a navigation system is the quality of the maps. The two main suppliers of mapping data are NAVTEQ and Tele Atlas. Both companies have made great strides in this area, but NAVTEQ is still the best choice for North America. As of this writing, NAVTEQ’s maps are more accurate and complete than Tele Atlas.

   Number of POI’s – In GPS speak, a "Point of Interest" is a business address saved on the GPS. You can think of the POI database as a pre-loaded yellow pages. Most modern GPS devices come pre-loaded with a Points of Interest database, allowing you to find nearby businesses, such as restaurants, gas stations, hotels, and more. Some less expensive GPS units ship with as few as 750k POI’s, while more expensive units can have up to 8 or even 10 million.

   Routing Quality – Even if two GPS units have identical maps installed, they may choose very different routes. That’s because there’s a lot of math and algorithms behind how GPS devices figure out the “best” route to your destination. Is a particular street closed after business hours? Will you arrive only to find your destination is on the left side of a busy street, and you have to make a U-turn or go around the block? Is a given highway known to be congested at this time of day? Is a slightly longer route actually a shorter drive time? These are all factors that GPS manufacturers must tackle, and some do a decidedly better job than others. This is the least well understood aspect of GPS devices, and not something advertised on the box. Be sure to check out our reviews and find out which GPS devices get this right. In general, Garmin does the best job routing, followed by Magellan, and then TomTom.

   Ease of Use – How easy is the GPS to use? Could you loan it to a friend and have them use it without any help from you or the instructions? Before buying a GPS, test it out (or read our in-depth reviews on this site) and try to input a destination address, search for a POI (point of interest), and take a look at the map screen. These are the basic functions you’ll want to check out to test ease of use.

   Mounting Hardware – It sounds like a minor issue, but all too frequently even the most promising GPS can turn into a lemon when the mounting hardware doesn’t work well. Beanbags, windshield mounts, flex-arms, and adhesive mounting discs are just some of the various methods companies use. Look for a mount that doesn’t vibrate while driving, stays connected to the windshield, and is easy to dock/undock the GPS.

   Nice to Have’s – Depending on your budget, features you may want (but aren't critical for basic navigation) include:

   • Larger Screen - Many GPS manufacturers now sell 4-inch widescreen GPS units. Though not essential, the wider screen does make things easier to see. Those looking for more portable units that can easily be stowed in a shirt pocket may prefer the more standard 3.5" display size.
   • Text-to-Speech - TTS, or Text-to-Speech makes it possible for the GPS to announce actual street names. So instead of hearing "Turn Right Ahead", you'll hear "Turn Right on Main Street".
   • Bluetooth - Bluetooth enabled GPS units can be paired to a Bluetooth enabled cell phone for hands-free speakerphone.
   • Traffic - Real-time traffic data is available on some GPS units (requires an annual subscription fee of around $65) and allows the GPS to make routing decisions based on current traffic conditions, avoiding accidents and tie-ups. Note that traffic coverage is generally only available in metropolitan areas, so be sure to check the coverage map before subscribing if your GPS supports this feature.
   • FM Transmitter - GPS units that have an integrated FM transmitted can route the GPS' audio to your car's stereo speakers via the FM radio (similar to many iPod car adapters that do the same thing). Quality varies, and long trips will almost certainly require you to change channels a few times to find an unused frequency on the FM dial. If your GPS has an audio out jack, you're better off using a cassette adapter or auxiliary audio hookup.

   **Be sure to check out the GPSmagazine Buyer's Guide for a complete list of all GPS rankings and reviews before buying your next GPS.

It's true that 90% of all gadgets are probably just a waste of money and do little more than the equipment you already own. But a GPS is a worth-while purchase that will enhance your life and quickly become an essential part of any travel plans.