Chip Bennett

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.

cbnet Different Posts Per Page

Customize the number of posts, orderby, and order parameters for all index pages (blog/home, search, category, tag, taxonomy, author, date, and archiv …

Adam Harley (Kawauso)

Adds a setting under Settings -> Reading to allow the front page post count to be controlled independently of the main post count and adjusts paging to accomodate for this.
Uses the <code>pre_get_posts</code> hook and checks for the <code>$wp_the_query</code> query being passed, so won’t work with <code>query_posts()</code>.

Set Front Page Post Count

Allows the front page to have a different number of posts than other pages.

cbnet Different Posts Per Page vs Set Front Page Post Count