American Airlines (one of the two, with United, whose planes were hijacked) aired this ad after 9/11. It's a good ad, seeking to rebuild confidence without boasting or downplaying a tragedy.
United Airlines aired this ad following 9/11; theirs was very different from American's but also good in similar goals. (I've always liked how United uses Gershwin's Rhapsody in Blue in different ways in their ads.)
Here's a commercial that Anheiser-Busch made in acknowledgement of 9/11; allegedly, they aired it only once because they didn't want to profit financially from it.