I've used Softerra's LDAP Browser for years; it's an excellent (free) tool, but it's only available for Windows. For the Gurubox project, I needed a similar package for a Linux platform. A little digging, and I found JXplorer; this LDAP-browsing tool originated with Computer Associates' eTrust Directory development team, but they've thrown it into the open-source world. A quick install--plus a few pokes at a public LDAP server (I used directory.colostate.edu)--showed me that JXplorer is a great tool for the LDAP detective. (Did I mention the 100-page user guide? Or that it "just worked" on both Ubuntu and WindowsXP?)
If you work (or play) with LDAP, this one's worth a look.