This is actally a tough one (and IMHO and important one). It is really hard to overstate the influence African-American culture has had on the overall (mainstream) culture of the USA. Not to mention I've got a question I'm thinking of asking that could really use this tag.
The problem with using
african-americans is that implies to me a people, rather than a culture. The tag would be much more useful if it could include the culture (eg: Jazz music, Blues music) which some people of other ethnic backgrounds often participated in, rather than just African-American people.
For that reason, I'm actually in this case happier with
african-american (an adjective, not a noun).
Formerly a lot of african-american cultural items were referred to as "negro", and many things from that era kept the name (eg: Negro league baseball, Negro Spirituals). However, that word is decidedly discouraged today for new terms, so using
negro as a tag would be a Bad Idea.