Component naming conventions
B = battery

C = Capacitor

D = Diode (including LED)

F = Fuse

H = Header connector

J = connector

K = relay

L = inductor

M = Motor

N = Network (containing multiple passive components - usually resistors or capacitors)

Q = transistor

P = Potentiometer (some people use this, I don't)

R = Resistor

S = Switch

T = transformer

TP = Test Point

U = chip or integrated circuit

V = varistor / MOV 

X = crystal

BR = Bridge Rectifier

Anyone who wants to add to this list, please feel free to do so.