I've done some in previous years, and I intend to do some more next year. The two tactics I had most success with were:

1. Writing articles for free distribution. You stipulate that the article must be used in its entirety, and at the end of it you put what's called a "resource box" which is your 4-6 line plug for whatever service or product you're pushing.

Apart from the viral aspect, this has the added benefit of building your credibility as an authority in your field.

2. Email alerts. The one I did for about a year was a virus and hoax alert. I'd keep an eye on the subject, and whenever a new 'big one' was starting to take off, I sent out a brief "Beware of XYZ" email. My email sig did the selling in this case.

I didn't overdo it though--people would hear from me maybe 1-2 times a month. It's a soft sell approach.

Both of these proved productive for me. Nothing dramatic, but certainly well worth the effort.