I managed to get very cheap OU fares CDG-ZAG (with LH codeshare) through degriftour.fr (part of lastminute.com now, but they weren't at the time).

A word of warning - if you have battery-powered devices that you carry with you, make sure you're not planning on travelling with hand luggage only. OU don't allow batteries to be carried on board (and are very insistent upon this, especially at ZAG).