We use PlaybackPro from dtvideolabs and have found it to be very smooth and reliable. It does run on a Mac and plays anything Quicktime can read. You can also adjust geometry before you play the clip so if you have a non standard aspect ration you can clean that up. It does run on a Mac only, but we like the robustness of the Mac. You cannot overlay titles, etc like you can with Pro Presenter.
We use it in our broadcast trailer for rolling commercials. (very, very important) We do run from solid state drives or even thumb drives so we do not have spin-up latency if the drive has powered down.