Continental allows one stopover and one open-jaw. One way to take advantage of this rule allows you to get a free one way ticket in the US. For example, if I was going NYC-TLV-NYC, I'll book the ticket NYC-TLV (as the destination)-NYC(stopover for a few weeks, moths,etc.)-LAX. Viola, free one way ticket to LA.
You can change the date of the last leg (NYC-LAX) for free within 21 days of the flight.
Similar stuff is allowd on US and AA.