Three new healthsprocket lists examine Mega Health Plan world. Two present the seven largest national plans with respect to revenues and medical membership (with UnitedHealth and Anthem finishing #1 and #2 respectively in both categories):
Mega Health Plans 1st Quarter 2015 Medical Membership in 1,000s (Pre-Merger)
Mega Health Plans 1st Quarter 2015 Revenues (Pre-Merger)

A Becker's Hospital Review list details major points on the Aetna-Humana merger:
Becker's Aetna inks $37B deal to acquire Humana: 5 things to know

Meanwhile, if you're in the mood to watch some video on such mega deals, HealthShareTV has five recent videos posted:
Breakingviews: Healthcare M&A's big bang
How Centene's Planned Acquisition Of Health Net Affects The Ratings
Will Aetna, Humana Union Impact Health Costs?
Aetna’s Humana Deal Puts Pressure on Cigna
Aetna and Humana CEOs on Merger Deal