Below is a list of cheatsheets & links i use a lot in everyday IT/Infosec, maybe useful to some people,  add some! =)

*nix

http://www.digilife.be/quickreferences/QRC/The%20One%20Page%20Linux%20Manual.pdf

http://files.fosswire.com/2007/08/fwunixref.pdf

http://files.fosswire.com/2008/04/ubunturef.pdf

http://tldp.org/REF/ls_quickref/QuickRefCard-A4.pdf

TCPDUMP

http://www.sans.org/resources/tcpip.pdf?ref=3871

http://planetozh.com/download/refcards/tcpdump.pdf

DLL injection ppt

http://www.bluenotch.com/files/Shewmaker-DLL-Injection.pdf

Nmap

http://www.bandwidthco.com/whitepapers/netforensics/nmap/NMAP%20REFERENCE%20GUIDE.pdf

IPtables

http://www.heagarty.com/iptables.pdf

IPV6

http://sans.org/resources/ipv6_tcpip_pocketguide.pdf

SANS Intrusion Discovery Cheatsheets

nix http://www.sans.org/score/checklists/ID_Linux.pdf?ref=3831

Win http://www.sans.org/score/checklists/ID_Windows.pdf?ref=3826

http://www.zeltser.com/network-os-security/security-incident-survey-cheat-sheet.pdf

Google Hacking

http://www.sans.org/mentor/GoogleCheatSheet.pdf

Win Scripting

http://www.microsoft.com/technet/scriptcenter/learnit.mspx#EFB

Oracle

http://www.red-database-security.com/wp/oracle_cheat.pdf

SQL injection

http://ha.ckers.org/sqlinjection/

XSS

http://ha.ckers.org/xss.html

Botnet Topology

http://www.csoonline.com/article/348317/What_a_Botnet_Looks_Like

Packetlife Cheatsheets

http://packetlife.net/cheatsheets/

BGP
EIGRP
IEEE 802.1X
IEEE 802.11 Wireless
First Hop Redundancy
IPsec
IPv4 Multicast
IPv6
IS-IS
OSPF
Spanning Tree
tcpdump
Wireshark Display Filters
Common Ports
IP Access Lists
Subnetting
Markdown
MediaWiki
MPLS
Quality of Service
VLANs
Cisco IOS Versions
Physical Terminations

Ed Skoudis’ Pentest Cheatsheets

Windows commandline tools
Netcat Cheat Sheet
Useful Attack Tools, Metasploit commands, HPing, FGDump

Nmap and CEH Mindmaps – from Andrew Mason @ http://www.mindcert.com/resources/

http://www.mindcert.com/resources/MindCert_Nmap_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_Enumeration_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_Ethical_Hacking_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_Footprinting_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_Scanning_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_System_Hacking_MindMap.pdf

http://www.mindcert.com/resources/MindCert_CEH_Trojans_MindMap.pdf

http://www.mindcert.com/resources/CCNA_Cisco_IP_Routing.pdf