There has been a lot of discussion lately on mergers and takeovers amongst airlines. Here is a (likely incomplete) summary, excluding the DL/NW merger which has been announced.
Merger with United Airlines, CO forum thread on merger talks called off.
Merger with American Airlines, US forum thread.
Takeover Brussels Airlines, LH forum thread.
Takeover bmi, BA forum thread.
I’m sure I’ve missed some threads, so if you have more to add please post a comment with a link.