Over on Abnormal Interests, Duane sings the praises of the New Athena Unicode Font. Another word in its favour for scholars of antiquity -- it has a fine Coptic font and so is ideal if you work on Nag Hammadi codices and so on. I have found it a lifesaver for constructing synopses of the Gospel of Thomas and the Synoptics, where one needs Coptic alongside Greek, and it is the best way I have found for getting things lined up properly without line-alignment going nuts and driving you mad, which happens when you combine different fonts in Synopsis.
Update (22:14): In comments, Jon recommends Antinoou: A Standard Font for Coptic. I have downloaded and given it a whirl and it's definitely a nice looking Coptic font and in many respects superior to New Athena Unicode. Its Greek is a little less pleasing to the eye, but it does render my Greek / Coptic Synopses of Thomas and the Synoptic successfully, so it is going to be a competitor to New Athena -- no question.