C706 is the primary specification for DCE/RPC 1.1. This document describes the concepts, protocol and internal mechanisms of the RPC architecture.
The Open Group also has the DCE 1.2.2 documentation set available for purchase. This contains some useful RPC information, particularly in the Application Development Guide.
Since DCE/RPC is the basis for Windows RPC implementation, Microsoft provide a lot of useful documentation.
Windows extensions to the DCE/RPC protocols are documented in MS-RPCE.
The Remote Procedure Call section of MSDN provides a wealth of information about the Windows RPC implementation.
The O’Reilly Microsoft RPC programming guide is a nice introduction to RPC programming on Windows. Most of it can be directly applied to DCE/RPC just by changing the function names.
The RPC Internals document is dated and incomplete, but provides a useful insight into some of the source code architecture and conventions.
The porting guide contains some historical information about porting DCE/RPC to new platforms. It’s not particularly relevant anymore, but it occasionally explains some of the rationale for the strange things that you find in the source.