Be careful as you look. One of the major rental car companies used to claim "no drop fees", but in reality built them into the rates (i.e. you'd get a much higher rate for the car for a drop-off than for a local rental). At CVG, Avis used to prohibit one-ways, but National allowed them for nominal cost.

If you've got a national contract (either company or something like USAA/AAA/etc) the drop fees are often negotiated as part of the contract.