Facebook & Twitter – announce/tweet/retweet interesting topics, newsflashes (yours and others if relevant to your followers/friends), info updates / additions to the website.
Youtube – tips for customers e.g. here’s something you can try at home. This is a nice personal advertisement which can also be added to your own website. Any videos of you at work.
Forums – giving helpful advice and getting involved in discussion can give you added credibility. Becoming involved in a few online communities which are highly relevant to your business
Emailing list – add any new contacts, prospective and existing customers (people who you have had dealings with). Do not collect email addresses from the internet and spam people. Regularly email in a standardised format, and always from the same email address.
Although these methods keep you connected with people, any links to your site will not be counted by search engines. Those links are still valuable advertisements which can lead people directly to your site.