I found a post that I consider merely spam.
What should I do? Should I down-vote the spam, remove the spam link, or post a question on the meta site to ask them to delete the spam?
When you see spam posted on a Stack Exchange site, you should click on the flag link, and select spam from the dialog that appears.
When 6 users flag a post as spam, the post is automatically deleted. Moderators will then destroy the spammer account.
Don't down-vote spam: The spam flag causes the post to be automatically down-voted. Unlike ordinary down-votes, this automatic down-vote won't subtract points from your reputation.
Don't edit links from posts that are spam: This makes difficult to individuate spam.
If the post is an answer, and it has been effectively written to answer the question, moderators could decide to remove the link and leave the answer. In the case the answer is suggesting a module, or a specific tool, and the user keeps suggesting the same module/tool for every similar answer, it is probable that one or more answers are removed.