Monarch are operating the following during the Winter using A330s;
These are regualarly operated in the summer;
You will also find that a lot of European charter carriers operate triangular long haul routings. For example, I know that Condor operate the following;
Thomson Airlines and Thomas Cook will also be operating triangular flights, most likely through Caribbean islands, especially Cuba and the Dominican Republic.
Virgin Atlantic are another airline that I belive operate triangles through the Caribbean.
I'm also booked on a tringular routing for February. To travel from Buenos Aires to Ushuaia, I am flying the following;
These flights are with Lan Argentina.
[Edited 2010-01-04 14:28:29]