1) Area code info
Example: http://www.google.com/search?q=414
You'll get a map of where the area is located. I checked area code 847 (Chicago's northern suburbs) and got a map that showed portions of four states near Chicago. Not very useful.
2) Universal Product Codes (UPC)
Example: http://www.google.com/search?q=073333531084
3) Vehicle ID (VIN) numbers
4) U.S. Postal Service tracking numbers
5) Flight Tracking
Flights to and from the U.S. Note: Many services like those linked from Google exist and have existed for many years. Some of you might also want to take a look at this tracking service. I checked flights from several airlines with this new Google feature and got nothing. Airlines that I didn't find links for included Jet Blue, Southwest, AirTran, Midwest Express, Sun Country, Spirit, ATA, Lufthansa, Virgin, KLM, Aloha, and Hawaiian. It also appears that single digit and some four digit flight numbers do not work. It's surprising that Google didn't check this before releasing this shortcut and making the announcement. SearchDay reports that Yahoo has also added flight tracking shortcut."