I came across the Religious Affiliation of Comic Book Characters in my wanderings while home sick from work today. I noticed a few interesting details:
1) The majority of human superheroes are Christian.
2) The vast majority of villains are anti-religious, areligious, or atheist.
3) There's only one listed character who has even a tenuous link to Celtic practices.
The first two don't surprise me, but I think the writers are missing some real opportunities by pandering to mainstream American assumptions like that. The third has me relieved. My Asatruar friends have enough of a love-hate relationship to Marvel's depiction of Asgard's finest as it stands. I'm not sure I want to seek out anything depicting Dr. Druid, though. The description on Marvel's site is more than enough for me.