Here are some interesting cheat sheets that people posted in the Pentest mailing list:
Networking cheat sheets:
- Protocols: Spanning Tree, Ipv6, Ipv5, OSPF, EIGRP, BGP
- Applications: Tcpdump, Wireshark
- Reference: Common ports, IP access lists, Subnetting
- Technologies: MPLS, QoS, Vlans, IOS version
Linux-Unix Command Line sheets:
The name says all.
Here are very good quality cheatsheets, this site used to be "IloveJackeDaniels".
- Regular expressions
- SQL SERVER
- Ruby on rails
A very big collection of many cheat sheets, you can find things like: