RFC2481 - A Proposal to add Explicit Congestion Notification (ECN) to IP

Experimental RFC.
http://www.rfc-editor.org/rfc/rfc2481.txt

BCP28 - Enhancing TCP Over Satellite Channels using Standard Mechanisms

Best current practices document describing ways to improve TCP performance over satellite links.
http://www.rfc-editor.org/rfc/bcp/bcp28.txt

RFC2883 - An Extension to the Selective Acknowledgement (SACK) Option for TCP

Proposed standard.
http://www.rfc-editor.org/rfc/rfc2883.txt

RFC2988 - Computing TCP's Retransmission Timer

Proposed standard.
http://www.rfc-editor.org/rfc/rfc2988.txt

RFC2581 - TCP Congestion Control

Proposed standard set of congestion avoidance features in a TCP implementation.
http://www.rfc-editor.org/rfc/rfc2581.txt

RFC1323 - TCP Extensions for High Performance

Defines TCP Window Scale option, timestamps, and protection against wrapped sequence numbers (PAWS).
http://www.rfc-editor.org/rfc/rfc1323.txt

RFC2582 - The NewReno Modification to TCP's Fast Recovery Algorithm

Experimental.
http://www.rfc-editor.org/rfc/rfc2582.txt

RFC2018 - TCP Selective Acknowledgement Options

Defines SACK (a technique to better recover from multiple packet losses per round-trip time interval).
http://www.rfc-editor.org/rfc/rfc2018.txt

RFC793 - Transmission Control Protocol

The original TCP definition. Also STD7.
http://www.rfc-editor.org/rfc/rfc793.txt

RFC2861 - TCP Congestion Window Validation

An experimental RFC that addresses revalidation of TCP congestion window after a period of time when connection wasn't network-limited.
http://www.rfc-editor.org/rfc/rfc2861.txt

RFC3042 - Enhancing TCP's Loss Recovery Using Limited Transmit

A standards-track set of changes to TCP that decreases reliance on the retransmission timer.
http://www.rfc-editor.org/rfc/rfc3042.txt

RFC3168 - The Addition of Explicit Congestion Notification (ECN) to IP

A two-bit IP packet header field that allows to reduce the number of TCP retransmissions in the Internet.
http://www.rfc-editor.org/rfc/rfc3168.txt