There are several tools. You might want to check out:
Apache Directory Server/Studio - an LDAP browser and directory client for Linux, Mac OS X, and Microsoft Windows, and as a plug-in for the Eclipse development environment.
JXplorer - A Java-based browser that runs in any operating environment.
LDAP Account Manager - A PHP based webfrontend for managing various account types in an LDAP directory.
phpLDAPadmin - A web-based LDAP administration tool for creating and editing LDAP entries in any LDAP server.
I have had the most luck with phpLDAPadmin. Its the easiest to use but requires some time to setup. It all depends how in depth your needs are.