Ancestry.com’s UK site has posted slave registers from British colonial dependencies for the years 1812-1834.  Although on the UK site, they are accessible from Anncesrty.com in the U.S.  The site is here.  The site is free. I first had heard that there was some registration requirement, but I went to the site directly without even signing into my Ancestry.com account.

Read more about British colonial slave registers at the UK National Archives wiki, Your Archives.

Craig