MapQuest published a free AppExchange App that's worth checking out. It plots accounts and contacts from Salesforce, and can also run proximity searches to find nearby matches.

As a sales person you might use it to look for reference customers in the area. You can imagine a rep on the phone saying, “Hey Doug, are you familiar with a company called XYZ Corp? I think they might even be on your same block. We’ll they’re a customer of ours who have had great success with the product. I’d be happy to put you in touch.”

If you’re traveling this could also be a good way to find other customers in the area so that you can stop by and pay them a visit.

Give it a try!