The sources for the following reference cards is on Github.
Periodic Table of Elements
Last updated: 2018
Contains atomic weight, mass number for most abundand isotope, atomic number, full electron configuration, valence electrons, and nuclear spin of most abundant isotope with I≠0.
Modern Fortran Reference Card
Last updated: 2015
Reference card for Fortran 90/95, with select features of Fortran 2003/2008.
Contents: Data Types, Control Constructs, Program Structure, Intrinsic Procedures, Input/Output
Vim Reference Card
Last updated: 2010
Contents: Movements; Insertion & Replace; Deletion; Insert Mode; Search & Substitution; Standard Mode Formatting/Filtering; Visual Mode; Undoing; Repeating & Registers; Copying; Patterns; Spell Checking; Marks, Motions and Tags; Multiple Files / Buffers; Scrolling & Multi-Windowing; Misc Ex Commands; Ex Ranges; Completion; Folding, Compiling, Miscellaneous.
Python 2.5 Reference Card
Last updated: 2009
Contents: variable types (numbers, sequences, sets, strings and regular expressions), basic syntax, object orientation and modules, exception handling, system interaction, input/output, standard library
Perl Reference Card
Last updated: 2008
Contents: variable types, basic syntax, references and data structures, system interaction, input/output, regular expressions, object-oriented perl and modules, and one-liners.
ASCII Table
Others
The following reference cards are less polished than the above: