(This little screed has gotten hundreds of shares on FB. I thought I'd post it here, being timely for the weekend.)
Attention Pagans - repeating this makes us look stupid. This stuff comes from half-wit anti-Catholic literature of the 19th century - it is worthless in light of modern scholarship.
Let's do this in a little detail:
1: Ishtar is not pronounced 'eester' - silly. If one pronounces a long 'I' one can arrive at "eeshtar', but that's only so close. In any case see below for the origin of 'Easter'
2: Ishtar was a goddess of fertility and sex, also war and sovereignty. While the Spring equinox season was important, it was not her particular feast. In any case the Feast of the Resurrection has only a coincidental association with spring equinox.
3: There are no depictions of Ishtar with eggs or rabbits. These symbols might be associated with the Germanic goddess below, but not with Ishtar, who has no relationship with the Christian feast.
4: Constantine did not Christianize the Roman empire. He made Christianity legal and was, to some extent, a patron of the early church. My impression is that there was no active worship of the ancient goddess Ishtar in Constantine's day.
Most specifically, the name of the goddess "Ishtar" has nothing to do with the Germanic name of the Christian feast, 'Easter'.
Easter was said by the early medieval scholar, Bede (and only by him) to be derived from the English goddess-name Eoster. That name is hard to trace, though a bit of progress has been made. It occurs elsewhere hinted at in place-names, and in literature only as a name of the month of April - 'Ostaramonath' or 'Eastermonath', which may just mean 'Easter Month'. A germanic goddess-name of that sort would be connected with goddesses of dawn - Eos in Greece, etc. The most likely meaning for the name 'Easter' for the Christian feast is "the feast we keep at dawn".
Most of the Christian world does not call the Feast of the Resurrection 'Easter'. In most languages it is called some variant of 'Pascha', derived from the Hebrew 'Pesach' - the Passover feast. Only English speakers call it "Easter" (and German Ostern) - nobody in Rome ever called it that. Constantine surely never heard the word "Easter", which would not have been invented for several hundred years after his time.
Summary: There may be pre-Christian remnants in the folk customs surrounding the Christian Resurrection Feast, but they have nothing to do with the ancient goddess Ishtar.