The 265t comes with a traffic alert receiver and a subscription to Navteq traffic alerts. If you go to http://the-portable-gps.com you can get comparison charts on all current and discontinued Garmins. The chart will compare the features of each unit.
The 265WT has blue-tooth and traffic alerts while the 255W does not. I don't think there is 255WT although a cable to give traffic alerts can be added to a 255W.
The 265T includes free lifetime traffic.