Links.

1. CCIE R&S Troubleshooting Lab 1 for GNS3
Just great lab.

2. Multipath Load Sharing with two ISPs
Faced this issue recently.

3. IPv6 Prefixes
Dynamic IPv6 statistics.

4. EtherChannel considerations
Because official cert guide is too poorly written.

5. Dsniff
"dsniff is a collection of tools for network auditing and penetration testing" . Nuff said.

6. Sniffing on IOU
Because you need it.

7. Process, Fast and CEF Switching and Packet Punting
Feel the difference.

8. Charles Spurgeon's Ethernet (IEEE 802.3) Site
All you need to know in one place.

9. Network Engineering beta
"Network Engineering Stack Exchange is a question and answer site for network engineers. It's 100% free, no registration required."

10. Creative Routing Contest
Already completed but still pretty interesting.