I am working on setting up a blog for my website. It is better, for rankings, to host the blog on a seperate domain name or have it as a subdomain of my current site? Thanks Andy
If the blog is about your current site's niche then as Sam suggested is best. If it has nothing to do with your main site's niche then of course a new domain would be the choice.
For rankings use a separate domain, for branding use a subdomain. A subdomain is considered another domain anyway, but it's harder to rank a subdomain as it holds less weight than a tld.
I would recommend website.com/blog, because it will help website to be crawled frequently and back links to website.