For those who are interested, here is the latest freely available draft of the C standard, C11:
Here is the latest freely available draft of the previous version of the C standard, C99:
The above documents can be found at "the international standardization working group for the programming language C":
You may be able to find a copy of the C89/C90 draft standard here:
Please send a personal message to a moderator if you feel something should be added to this list of C standards.
And thank you Quzah for doing just that before I added this.
And another thank-you to cwr.