etspring

NEW: Supports built-in WordPress comments threading! [see notes 2 and 3]
Automatically synchronizes comments from Your LiveJournal blog with Your stand-alone WordPress-based blog.
All imported comments are associated with Your blog entries, crossposted to LiveJournal, and shown along with comments, written in You blog.
You can choose how often do the synchronization.
Synchronization does not slow down loading of Your pages, everything is done in background.
Note 1: This plugin has to be used together with LJXP (LiveJournal CrossPoster) plugin. Support of JournalPress and other crossposters will come in future versions (please feel free to post feature requests at the plugin homepage).
Note 2: Threading depth is limited by WordPress settings (<code>Settings - Discussion</code>).
Note 3: You should consider removing <code>Reply</code> link for imported comments, because they are not really a part of WordPress :).

LJ comments import: reloaded

Automatically synchronizes comments from Your LiveJournal blog with Your stand-alone Wordpress-based blog.

chherbst

This plugin synchronizes information of an Semantic Media Wiki 
with a wordpress blog.
It is supposed to be used in production without any downtime of the site. 
The way SMW data is imported can be configured using a simple php mapping array.
Until now it supports importing poss, categories, attachments, meta data, links and full galleries. Only data which has actually changed will be imported, thus minimizing the 
time on successive imports.
The supported import format is JSON. Thus it could also be used for data sources other than Semantic Media Wikis, as long as they export their data in JSON format.

SMW Import

Plugin to synchronize a wordpress blog with a JSON source, e.g. a Semantic Media Wiki.

LJ comments import: reloaded vs SMW Import