UPDATE (Oct, 2014): JConverter 1.5 supports import of images from Wordpress to Joomla. It also supports importing same URL alias from Wordpress in Joomla so you can keep same URL in new site with minimal changes.
UPDATE (Jan, 2014): JConverter 1.4 supports importing comments from JComments for 3.x version now.
UPDATE (Sep, 2013): JConverter now Joomla 3.x compatible and is available as part of the JConverter download package. Please note that 3.x compatible version does not support import of comments from Wordpress since JComments is not yet compatible with 3.x.
JConverter is now 2.5 compatible with many bug fixes and some awesome new features. Here are some new features added in 2.5 version.
1) Supports importing nested categories from wordpress.
2) Associates posts with categories in Joomla after imports.
3) Supports JComments integration for importing comments.
4) Supports setting a new password for users while importing users.
As the name suggests, JConverter allows you to convert your WordPress blog into a Joomla site. It can import users, blog posts, categories, pages and even links from your WordPress blog to Joomla.
It's very easy to use. Just install it, select the options you want to imports from WordPress and click on "Start Conversion". It queries the WordPress database for blog posts, pages, users, links and categories and converts them to Joomla format. All in just one click.
This is BETA release and there are some new features planned in future. As of now, there are certain limitations of JConverter which you can find under configuration panel of component.
IMPORTANT : Though you can import your WordPress site in an existing Joomla site, it's ideal for creating a fresh Joomla site from an existing Wordpress site. In such case, install the latest Joomla version WITHOUT SAMPLE DATA, install JConverter, provide the configuration details and import.
This extension is built on top of mtwMigrator to avoid reinventing the wheel since it was very close to what was needed for JConverter. Thanks to Matias Aguirre for building such a useful extension.