Acid-base indicators are classified into 3 different groups: phthaleins and sulphophthaleins, azo indicators, and triphenylmethane indicators. The two most common indicators used in acid-base titration are phenolphthalein and methyl orange. Phenolphthalein can be used for strong acid-strong base titrations as well as weak acid-strong base titrations. Methyl orange can be used for strong acid-weak base titration. For weak acid-weak base, there is no indicator that is suitable for this titration.
Examples of indicators for each type of titration: