Novell's Alternative to System.DirectoryServices
Novel has released a .NET based library for LDAP operations [1]. Unlike Microsoft's implementation, this is pure managed code, so you won't have to deal with those amazingly informative “Error 0x85000000“ errors that Microsoft's Win32 API wrappers in the System.DirectoryServices namespace love to give you. Some cool features in there too, like async support. And I must also mention, that you can also download the complete C# source. [2]
[1] http://www.novell.com/coolsolutions/cooldev/features/a_net_cplus_ldap_library_cdev.html
[2] http://forge.novell.com/modules/xfmod/cvs/cvsbrowse.php/ldapcsharp/CsharpLDAP