These are the strong acids. What makes them 'strong' is that they completely dissociate into their ions (H+ and an anion) when they are mixed with water. Any other acid is a weak acid. There are only six strong acids, so you might want to commit the list of strong acids to memory.
HCl - hydrochloric acid
HNO3 - nitric acid
H2SO4 - sulfuric acid
HBr - hydrobromic acid
HI - hydroiodic acid (also known as hydriodic acid)
HClO4 - perchloric acid
As the strong acids become more concentrated, they may be unable to fully dissociate. The rule of thumb is that a strong acid is 100% dissociated in solutions of 1.0 M or less.