I agree with the other answers on specifics - taken collectively they are a great set of ideas for building client trust.
There is absolutely nothing you could give me as a freebie that would "amaze" me. Quality work, clear communication, and fair prices and schedules amaze me. Free stuff of any ilk does not. In the end, I know that any free stuff you give me will be paid for by overhead carved from the money I paid by being a client. Unless you have a money-generating machine in your basement, you're not going to make my jaw drop.
The best marketing scheme for me is writing really good newsletters or blog posts. By really good, I mean it has to be insightful, easy to read, highly relevant and not too frequent. For me, monthly is the maximum. Quarterly is just fine. I've stayed in contact with a number of consultants of various types simply because I got useful information from enough of their blog posts that it was worth it to stay subscribed. Then, when I'm thinking about the topic, voila!, there they are with applicable content for my search criteria.
But I can't emphasize enough how important it is that you be able to write something interesting and useful. If you fail at this, you become spam and your recipients will unsubscribe, block you, or simply filter you out, mentally.