Enjoy some of the quick reference cards which I frequent.

• Coding in C -- C_Card.pdf, C_Card.ps
• GNU Debugger (gdb) -- GDB_Card.pdf, GDB_Card.ps
• Cascading Style Sheets (css) -- CSS_Card.pdf, CSS_Card.ps
• Concurrent Versions System (cvs) -- CVS_Card.pdf, CVS_Card.ps
• Standard Template Library (stl) -- STL_Card.pdf, STL_Card.ps
• Plain TeX -- TEX_Card.pdf, TEX_Card.ps
• UPS (Unix Product Service, a package manager from FNAL) -- UPS_Card.pdf, UPS_Card.ps

Here are some of the sources I've used to find these cards.

• refcards.com
• digilife.be