Offhand I don't know of anything aimed at the blog market that does LDAP out of the box. There are a [link|http://patcavit.com/2005/05/11/wordpress-ldap-and-playing-nicely/|couple] of [link|http://www.weblogs.uhi.ac.uk/sm00ay/?p=45|methods] for doing LDAP with [link|http://wordpress.org/|WordPress], though, and it's GPL and extremely easy to install and configure.