So much of this depends on your target audience. Around here, Chamber of Commerce luncheons are great places to network. Of course there are plenty of other organizations as well like Yellow Tie, BNI, the Regional Commerce and Growth Association and so on.
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The best way to advertise your web hosting is finding a niche and targeting that particular audience. As you know Web Hosting is a huge field and toughest market, hosting/advertising with a niche will always lead you on success.
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No amount of advertising will ever beat out the accolades of satisfied customers spreading the word about you. Incentivizing your happy customers to spread the word will do far more than any ads ever will, but if you have something unique and special to offer and you want to advertise somewhere, might I suggest... here on WHT?