I can across this great infographic today (on the Australian Marketing Results website) which shows 40 different types of proof that you can put on your website (or publish in other material or just talk about) to back up the propositions or claims you are making to prospects.
Remember to choose the elements that will most appeal to your target audience (e.g. facts and figures for finance people) and to have a combination of emotional and logical appeals. The best proofs combine both (e.g. a customer testimonial telling their own story and how it has helped them personally backed up by the facts about the improvement they realised)