I just saw a pointer to a site I had to pass on here...

http://soliton.vm.bytemark.co.uk/pub/cpt-city/

To quote:
An archive of colour gradients

For cartography, technical illustration and design. The archive supports several formats and is organised by author.
These have been all converted to cpt, ggr, grd, inc, and svg.

There are a lot for topography, bathymetry, elevations, shaded relief.... I'm still looking through them!

-Rob A>