www.aircraftbooking.co.uk
Not free (about£49 p.a. I think, but has lots of add-ons, text alerts etc)
Also rapid personal service from owner if any probs.-we've used it since it started IIRC about 9-10 years with rarely any probs.
But if you really don't want to spend anything there are loads of freebees about.
Cusco