Links:
BGP
CIDR Reports - What's happening on the Internet as far as size of the BGP Tables and stats
Traceroute.org - Launch a traceroute from a variety of locations
Zebra - Routing software for a Linux that looks like a Cisco router
Route Views - University of Oregon Route Views Project - public access to a BGP Internet Router
MCI Internet maps - Marcomedia
EIGRP/OSPF/ISIS
EIGRP White Paper - A paper on Cisco's site on how it really works
OSPF RFCs - A list on Cisco's web site for all the RFC
OSPF Design Guide - Another Cisco paper
ISIS Standards - A list on Cisco's web site for all the RFC
ISIS NSF - Cisco white paper on non-stop forwarding & tuning the timers
ISIS Tips - Cisco samples & tips on configuring ISIS
IP Version 6 - A list of white papers & configuration guides and examples for IPv6
Router God (has an interesting twist on explaining technology on Cisco routers)
Cisco Systems In A Nutshell (This guy has sent a lot of time setting links to a lot of useful sites...all about Cisco)
Network Designs NW (Technical forums have some good basic information)