A relatively new feature of Google Maps is Street View. For the last few years, Google has been sending cars equipped with special cameras down the world's streets, capturing everything one can see from that perspective. By dragging the "Pegman" icon onto a Google Map, you can see any Street View images recorded there. Is the address you have for your suspect an empty lot, a mail drop, or a house? By using Street View, you probably won't have to ask someone to drive by there to find out.
Another free service, and one I find especially cool, is Google Voice (GV). You sign up for a free GV account and choose a GV phone number, or assign the service to your existing mobile phone number. On your GV page, you tell GV what numbers to ring when someone calls your GV number. You might include your home and cell, and maybe include work, a friend's house where you'll be visiting, or a hotel you're staying in. You can change these at any time.
When someone calls your GV number, all of the listed phones ring at the same time. The call is routed to the one picked up first, and the other numbers stop ringing. If you like, you can have GV ask for the caller's name before the call is connected, so when you pick up, you’ll hear "Call from Joe Blow." You can press "1" to accept it, or "2" to send it to voice mail. That option allows you to hear the caller record the voice mail message, and you can connect and speak to the person if you like.
When you have voice mail, Google's auto-transcriber takes its best shot at converting the message to text, and e-mails it to the account you specify. You can also get it sent to a cell phone as a text message. You can specify "do not disturb" periods when everyone gets sent to voice mail, and create individual outgoing messages for specific numbers.
The service does a lot more than what I've described, and you may or may not use all the features. It’s still a valuable resource for staying in touch with the people you need to connect with, and avoiding everyone else.