A company that I think many consider less than interesting on HN is "ITA Software," who is solving the age-old O(n) problem of a million ways to purchase a ticket and have made traditional travel agents obsolete (e.g there are 400 x 400 different combinations for BOS to SFO round trip, so 160,000 different ways to fly a round trip ticket, plus 10,000 for fare conditions and booking classes, resulting in 1.6 billion possible combinations). They're the people that power Orbitz, United, Continental, Southwest, Air Canada, and so forth. And they also power HN beloved Hipmunk.