This plugin will allow you to customize the number of posts, orderby, and order parameters for all index page contexts, including the blog posts index, search index, and all archive indexes (category, tag, taxonomy, author, date, archive). Orderby settings support all values relevant to archive index pages, including none, ID, author, title, name, date, modified, rand, and comment_count. Order settings support ASC and DESC.
Note: Plugin settings can be configured via Dashboard -> Settings -> Reading.
This plugin is available for download for your site.