Delta: For first time transfers only: 50% bonus miles on American Express reward transfers through September 30, 2011. Similar to the promotion they ran this past Winter/Spring, transfers of 100,000 points or more will give you 25,000 MQMs towards status (although the past promotion only required 50,000 points). 25,000 MQMs will automatically give you silver status through February 2013. Must register first prior to transferring any points over.
If you have already transferred to Delta in the past, you can still qualify for the 25%-40% bonus offer, which I wrote about here. Unfortunately, this promotion will not grant you any MQM miles and runs until June 30, 2011. For both promotions, it has been noted that bonus miles transfer immediately, although the T&C state otherwise. Also, you can put a Delta redemption flight on hold for two days while you are waiting for your miles to transfer over.
British Airways: 50% bonus miles on American Express reward transfers through July 31, 2011. This is only for U.S. members of the American Express Rewards program. Only your first transfer is eligible for the promotion, so make sure to transfer the number of points during the same transaction. Keep in mind that British Airways can have some pretty hefty taxes and fees with reward redemptions, especially for flights originating in Europe. Click here for a previous post regarding redeeming British Airway miles.
Virgin Atlantic: 25% bonus miles on American Express reward transfers through June 30, 2011. The details state that the bonus points will take up to 14 days to post. Also note, similar to British Airways, there are many times high taxes associated with award redemption.
Additionally, American Express is currently offering great promotions for new credit card applicants. You can then transfer the earned points to the bonus offers above.