Check out this link: http://www.rubyinside.com/ruby-style-guides-and-tools-how-to-write-good-looking-ruby-1272.html

It highlights two useful posts about Ruby style (here and here) and includes a link to reek, a popular tool for sniffing out code smells.

UPDATE: also, check out towelie: http://gilesbowkett.blogspot.com/search?q=towelie