I have the same problem - I'm required by my employer to take the lowest-priced 'reasonable' flight, regardless of brand loyalty.

We book our corporate travel with Egencia (the corporate arm of expedia). When I make a booking it's emailed to someone in finance for approval, and they're alerted if there are cheaper options I could have chosen.

I think in this 'economic climate' we'll see more and more of this sort of thing.

I don't really mind - Unlike some of my colleagues at least I still have a job.