Community Wiki: How can I prevent comment spam on sites which I control?
The topic of spam prevention comes up fairly often, but the answers which are provided aren't consistent (because everyone has his or her own favorite solution).
To ensure that askers see all the options at their disposal, I've put together this catch-all question (note that questions about using specific spam prevention tools should still stand on their own - this is more for "what should I do about spam?" questions).
Please take this opportunity to contribute your own spam prevention solutions/recommendations and vote up this community wiki Q/A so askers have a chance to see it before they post a "what should I do about spam?" question.