The following requests for comments provide interesting background information:
RFC3383: Internet Assigned Numbers Authority (IANA) Considerations for the Lightweight Directory Access Protocol (LDAP)
RFC3377: Lightweight Directory Access Protocol (v3): Technical Specification
RFC3296: Named Subordinate References in Lightweight Directory Access Protocol (LDAP) Directories
RFC3112: LDAP Authentication Password Schema
RFC3062: LDAP Password Modify Extended Operation
RFC3045: Storing Vendor Information in the LDAP root DSE
RFC2927: MIME Directory Profile for LDAP Schema
RFC2891: LDAP Control Extension for Server Side Sorting of Search Results
RFC2849: The LDAP Data Interchange Format (LDIF) - Technical Specification
RFC2820: Access Control Requirements for LDAP
RFC2798: Definition of the inetOrgPerson LDAP Object Class
RFC2739: Calendar Attributes for vCard and LDAP
RFC2714: Schema for Representing CORBA Object References in an LDAP Directory
RFC2713: Schema for Representing Java(tm) Objects in an LDAP Directory
RFC2696: LDAP Control Extension for Simple Paged Results Manipulation
RFC2596: Use of Language Codes in LDAP
RFC2587: Internet X.509 Public Key Infrastructure LDAPv2 Schema
RFC2307: An Approach for Using LDAP as a Network Information Service
RFC's are available from http://www.ietf.org/rfc/ or your local mirror, for instance ftp://ftp.belnet.be.
When working on a Linux system, you may find most of these RFC's in the /usr/share/doc/openldap-<version>/rfc/ directory.