Social bookmarking sites such as del.icio.us and stumbleupon are valuable to your interactive marketing in two ways. First, they provide inbound links, improving your organic search rankings for certain keywords. Second, they serve as an unbiased user recommendation, and as such are a great form of word-of-mouth marketing.

A visitor who finds your site through a link on a social bookmarking site is predisposed to have a positive opinion, because they generally click on the links of their trusted sources for relevant information.

We’ve been studying the most recent crop of social bookmarking sites, rating them for their relevance to brand marketers. Here are the results:

1. Digg - Okay, technically, it’s not strictly a social bookmarking site, but more of a social news aggregator. Even so, there is a reason the term “Digg effect” has been coined. A front-page mention on Digg can bring a server-crunching volume of traffic to your company website.
2. Del.icio.us - It may not get many headlines these days, but by virtue of being one of the first social bookmarking sites, del.icio.us has a large, active user-base. Also, the newer versions of popular blogging software Wordpress come pre-installed with the ability to show the author’s “tag cloud” from his or her del.icio.us account, spreading the reach and popularity of the service.
3. StumbleUpon - This is a newer service that has a sort of random, “find the coolest sites you weren’t looking for” aspect to it. It’s seen a recent spike in interest and is growing in popularity.
4. Ma.gnolia - Another more recent addition to the social bookmarking space, this one is more popular with designers and graphic arts folks, thanks to its attractively-designed user interface.
5. Reddit - Can’t break into Digg? You might have better luck with Reddit, whose user-base is a bit friendlier to those who are openly promoting themselves.