We really liked our Kidco baby gate (we just took it down a few weeks ago). It was at the base of our stairs for the longest time - and then we moved it to Blake's bedroom door. He never tried to climb over it so I don't know how well it works for a climber but we really liked it. (we used the pressure mount which doesn't look like should be used for the top of the stairs). Here is their website:
http://www.kidco.com/main.taf?p=1