Here are some websites I've found offering free layouts for your Howrse account.
http://www.ebonygraphix.co.uk/layout_list.asp
http://www.horse-lover-layouts.com/index.htm
http://www.layoutsforhowrse.com/freelayouts.htm
http://howrse-layouts.webs.com/layouts.htm
http://www.capenetwork.com/howrse/layouts/free/homepage.html
http://www.allhowrse.com/freelayouts.html
http://www.freewebs.com/syvrana/layouts.htm
http://www.ebonygraphix.co.uk/layout_list.asp
http://www.horse-lover-layouts.com/index.htm
http://www.layoutsforhowrse.com/freelayouts.htm
http://howrse-layouts.webs.com/layouts.htm
http://www.capenetwork.com/howrse/layouts/free/homepage.html
http://www.allhowrse.com/freelayouts.html
http://www.freewebs.com/syvrana/layouts.htm