OK, before anybody completely freaks out, understand what that information on the activity list is actually telling you. This will only tell you what the direct connection was, which means that if a proxy server is used (pretty common, likely that's the Verizon IP modette is seeing), that's the address that's going to show up. Odds are it's probably in a different geographic region, so don't worry
too much, but definitely keep an eye on it.
What should be really concerning is if you see an IP from outside the country or if you see a concurrent session running. Close that session and immediately change your password.
Speaking of that, eliminate the word "password" from your vocabulary and change to "pass phrase". That's going to make it a lot easier to create strong passwords that you can actually remember.
Further more,
never store passwords in your browser (they can be read as plain text if you know where to look), never use a public PC (hotel, library, etc.) for anything that requires a password, and avoid public WiFi hotspots with anything that involves a password.
Finally, for anybody who is using Gmail, make absolutely sure that you are logging in using HTTPS, whether you are doing it from a browser or from a client. This is now the default, but that's a recent change. For those of you who have had accounts for a while, check your bookmarks or client settings:
Changing the HTTPS setting - Gmail Help