http://www.google.com/help/features.html#number

Tracking a package?

UPS tracking numbers example search: 1Z9999W999999999
FedEx tracking numbers example search: fedex 999999999999
USPS tracking numbers example search: usps 99999999999999999999


Look up a patent?

Patent numbers example search: patent 5123123


Look up an aircraft?

FAA airplane registration numbers example search: n199ua


Who made this old modem or video card?

FCC equipment IDs example search: fcc B4Z-34009-PIR