This rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of query warnings that it analyzed.
I am not longer maintaining
query_reviewier. Nathan has done a much better job keeping my plugin and idea up to date, please use his fork at the following location:
https://github.com/nesquena/query_reviewer
-David Stevenson http://flouri.sh