FYI: It's ILFC.

ILFC= International Lease Finance Corporation, the #2 aircraft lessor in the world, a unit of the insurance group AIG.
GECAS= General Electric Capital Aviation Services, the #1 aircraft lessor in the world, a unit of, obviously, G.E.
(Those rankings are usually based on fleet size. IIRC, GECAS's fleets tends towards smaller a/c, while ILFC's favors the big boys, so by dollar-value, the rankings might be reversed.)

Other major lessors include CIT, AWAS (Ansett Worldwide Aviation Services), debis (which is a unit of some big insurer, I think), Boeing Leasing, and Airbus Leasing. I've left out a few of the biggies, but that's because I can only think of those that one of my clients leases airplanes from.

Philip Morris (now part of Altria) has a lot of planes out there, as do many other big-name companies, such as the one shortfinals works for. Leasing was a great business for a while. Sept. 11th and the spate of airline bankruptcies that started in 2003 changed that. Things have improved substantially since then, and the business is performing well now, more or less. For some lessors, though, things are still pretty tough. There are a lot of airplanes still parked in the deserts of America and Australia.

As a rule of thumb, airlines often want to mix their fleets roughly 1/3-1/3-1/3 between straight ownership, lease-financing, and straight leasing. The rare airline, e.g. Southwest, buys all of its planes with cash and owns them outright.