Sometimes I come across symbols in circuit schematics that make me double take and say "what the...?" under my breath. Engineers seem to have a tendency to want to keep tweaking things even when they're "good enough", and the result is a huge variety of symbols used to represent even common parts.
There have been many symbol guides published online over the years, but "Electrical WHAT?!" is probably the best I've seen yet. Check it out at http://electricalwhat.com/