British Airways has a pretty lucrative promotion for transatlantic travel through May 31, 2013. You can earn 20,000 Avios per roundtrip transatlantic flight on American, British Airways, and Iberia, and an additional 100,000 Avios if you complete five qualifying roundtrips during the promotion period.
The catch is that only tickets in the following fare classes qualify (most of which are first/business/full fare economy):
British Airways: F, A, J, C, D, R, I, W, E, T, Y, B or H
American: F, A, J, R, D, I, Y, B or H
Iberia: J, C, D, R, I or Y
Registration is required prior to travel, and only tickets booked after the beginning of the promotion qualify. The bonus miles should post to eligible Executive Club accounts within four to six weeks.
This promotion period is only a bit over two months and you have to do five roundtrips to maximize the bonus (essentially earning 40,000 Avios per roundtrip), which is a lot. But if you travel to Europe anyway, this is an amazing promotion.
Given that the promo is also valid on American, I hope they match so one can earn AAdvantage miles instead. It might make some premium cabin fares to Europe pretty attractive for a mileage run.