What other standards are there than IEEE 315 and IPC?
IEEE 315, which you've already mentioned, is also known a ANSI Y.32.2. In addition there is ANSI/IEEE Std 91/91a/991 for logic symbols.
IEC 60617 (aka British Standard BS 3939) originally was used mostly for electromechanical drawings but has some electronic symbols as well and is a standard throughout Europe.
This document goes over some of the differences between standards, such as the difference between resistor symbols used in the US (IEEE 315) and Europe (IEC 60617):

This is the principal difference I have noticed when looking at various schematics on the 'net.