The Communist Party USA can't officially endorse a candidate, knowing full well if they do it would be like committing political homicide. But I was wondering which candidate they like so I thought I'd check out their web site. Their electoral policy page let's people know where they stand on the election.
While not specifically endorsing any candidate, about Obama they say "Barack Obama’s campaign has so far generated the most excitement, attracted the most votes, most volunteers and the most money. We think the basic reason for this is that his campaign has the clearest message of unity and progressive change, while having a real possibility for victory in November." That sounds like an endorsement to me.
They proudly state their slogan "People before profits" and their goal of a "Bill of Rights Socialism" say it all. Yes, that tells me all I need to know.