There's a great list over on Business2Community with 33 strategies and ideas for conversions. My top 5 out of the list would be:

• Checklists. When your prospective customer is looking for advice on a complex subject, the information can sometimes feel overwhelming. A straightforward and downloadable (thus printable) checklist from a trusted source will therefore feel fantastic. Create some and place them on a gated page so that you get their details.
• Templates. As with checklists, these provide great value to your prospects. Make sure they make sense for your business. i.e if you are website designer, a landing-page template could be a great way to open up a conversation with your prospects.
• Free tools. People like free things, especially if they are good. Buffer do this with Pablo, for instance, a free image-creating tool, which in turn makes their prospects more inclined to pay for their main social media management tool.
• Reports. In the B2B sector, reports on specific trends within your target industry are always popular. We create reports on content marketing in the legal, accounting, PR, and insurance sectors for instance.
• Popups. Are they irritating? Yes. Are they a great way to build your email newsletter? As we found out, yes.