From rfc 2900 Internet Official Protocol Standards:

Draft Standard Protocols
RADIUS     Remote Authentication Dial In User Service (RADIUS)     2865

Proposed Standard Protocols
--------   RADIUS Authentication Server MIB                        2619
--------   RADIUS Authentication Client MIB                        2618


Non-standard stuff:
Informational
2924 Accounting Attributes and Record Formats
2906 AAA Authorization Requirements
2882 Network Access Servers Requirements: Extended RADIUS Practices
2869 RADIUS Extensions
2868 RADIUS Attributes for Tunnel Protocol Support
2867 RADIUS Accounting Modifications for Tunnel Protocol Support
2866 RADIUS Accounting
2809 Implementation of L2TP Compulsory Tunneling via RADIUS
3162 RADIUS and IPv6
