Paul whatever you give away, I would make sure that it is FREE to you. But not necessarily the customer. Even if the cost to them is filling in an email address or getting details to sell them products later.
By giving information they are essentially telling you they are interested in your products. This is a great way to build a targeted mailing list.
Once a client is on your mailing list and happy to receive updates you can upsell your other deals. forever. 30% discount, limited time. ONLY 12 LEFT IN STOCK! etc
A really fantastic free item to give away is information/ebooks as suggested above. As it really is free, costs nothing to post, or share. But most importantly can be automated. How this can align with the rest of the business depends on the product and being a bit creative.
One-two punch. An instant one-time offer after getting the free promotion can work nicely too. - "Hey thanks for your interest in the 'free Widget promo' to say thanks, we are offering Red Widget for only XX in the next 24 hours. etc.
Good luck, and where's the link for free stuff!?