Because I'm currently doing a lot of non-programming tasks in emacs the spell-check problem became one of my major concerns once again.

I noticed that there is no question related to the options for spell-checking in emacs yet, so here we go:

What are my options to do spell-checking in emacs?

Specifically,

• for general purpose spell-checking, i.e. sensible suggestions for typos, spell correction of words
• for selective spell-checking, e.g. general purpose spell-check but only in comments
• for anything which I forgot or am not aware of but you can think of (spell-check related, duh...)

Edit: Forked off the "other" stuff in a separate question, What options are there for writing better texts in emacs