I want to continue to update my two Livejournal accounts – http://shankerbalan.livejournal.com and http://purple_dude.livejournal.com. Among the plugins I looked at, Journalpress worked best. It supported multiple accounts and was simple enough to use.
The other plugins which I tried are LJ-XP and Livepress. Livepress supports multiple accounts and has a whole bunch of settings which looked very useful to have but refused to work for me with WordPress 2.7.
LJ-XP on the other hand worked very well but supported only one Livejournal account.
The last plugin to try on my list was Journalpress. Journalpress was easy to configure and just worked with both my accounts. It is based on LJ-XP.
You can find more crossposting related plugins at http://wordpress.org/extend/plugins/tags/crossposting