What resources (books, Web pages etc) would you recommend that:

• explain the causes of latency in TCP/IP-over-Ethernet networks;
• mention tools for looking out for things that cause latency (e.g. certain entries in netstat -s);
• suggest ways to tweak the Linux TCP stack to reduce TCP latency (Nagle, socket buffers etc).

The closest I am aware of is this document, but it's rather brief.

Alternatively, you're welcome to answer the above questions directly.

edit To be clear, the question isn't just about "abnormal" latency, but about latency in general. Additionally, it is specifically about TCP/IP-over-Ethernet and not about other protocols (even if they have better latency characteristics.)