A way to capture remote traffic across the internet, when you're not on the same LAN as receiver or sender, is using BGP hijacking. Kapela and Pilosov gave a great presentation on this topic at Defcon 16: http://www.securitytube.net/video/173
The attack requires the attacker to have control over an AS. He can send false prefix announcements with favorable properties to his peers so that they will choose to route traffic for the victim via him. These announcements will propagate, and the attacker can capture a large portion of traffic (or even all) that was intended for his victim. To get the traffic delivered to the victim, the attacker needs to keep one of his peers 'clean' so he can hand the traffic off there.
The attack is complex and depends on a lot of factors. The internet is not a predictable place in terms of traffic flow. However, Kapela and Pilosov give a successful live demonstration of capturing traffic of the Defcon venue. Another famous example is Pakistan accidentally hijacking YouTube traffic in 2008 (http://www.circleid.com/posts/82258_pakistan_hijacks_youtube_closer_look). China has been accused of hijacking large portions of US internet traffic (http://bgpmon.net/blog/?p=282).
A way to secure against this is by using end-to-end encryption, like using SSL or IPSec. There are also some initiatives that attempt to make BGP more secure (SBGP, SOBGP).