Take your time. In the initial exhilaration of coming together, it's altogether tempting to want to name your new coven right away.
My recommendation is, don't. This is really far too important a decision to rush into.
Names are Wyrd-ful things. A coven name is aspirational, yes: but though it shapes what the coven will eventually become, it also needs to reflect what the coven already is. And sometimes that can take a while to "firm up."
So go slowly, and hold out for quality.
Avoid the humorous. Really, will the joke still seem funny 25 years down the road, after the ten thousandth repetition?
Probably not.