The verb "to be" has suppletion in many, many languages, IE and not.
In my native, Uralic, Hungarian the infinitive is lenni, from which are also formed the future leszek, leszel, lesz etc. and the imperative légy, legyetek. Other forms are from another stem altogether, beginning with v-: Present vagyok, vagy, van etc.; Past voltam, voltál, volt etc. Curiously, the conditional can use either stem: lennék, lennél, lenne etc. or volnék, volnál, volna etc.
The Romance languages do the same, with at least two, but more likely three stems. (e.g. French infinitive être, present ind. 1st pers sing. suis, preterite (becoming obsolete) fus. ) The first and second stems may be related etymologically, but this is hardly evident to the naive observer. Italian follows the same pattern, and introduces a fourth stem stato for the past participle. The Iberian languages follow the French pattern, but the infinitive ser is from a 4th root (Latin sedere) originally, although on the surface it looks as if it belonged with somos - son/são.
Seeing that we are all English speakers here, I don't have to elaborate on the suppletion of the verb "to be" in Germanic languages.
The verb "to go" also has suppletion in many languages, including English go/went. The Romance languages routinely merge the derivatives of Latin ire and vadere, to which French adds the derivatives of ambulare, Italian the derivatives of ambitare and Spanish/Portuguese merges in the equivalent of the preterite/pluperfect/past subjunctive of "to be" (i.e. Portuguese foi can mean both "he was" and "he went").
Hungarian jönni 'to come' has the suppletive imperative gyere.
Japanese widely uses suppletion for polite and highly formal verbal forms, with a complexity that I will simply not enter into here.