I used Van Zile Travel for several business trips. The agents were always courteous and very helpful. All I needed to do was state my requirements and an agent would email me back later that day with the possibilities. A very nice service that Van Zile offers for the professional traveller is the Travel Profile. While it takes a bit of time to fill out, the traveller's personal profile then stores all the important data that the agency needs to know, from hotel room preferences to all frequent flier numbers that you never have to worry about. Furthermore, a canceled ticket will be credited towards a new one purchased later.
They can be a bit expensive, though, as they charge a separate transaction fee for booking segments that cannot be booked separately.