The metaphor of the funnel is used because people drop away at each stage of a long sales process: for example, many of your unqualified prospects may have existing suppliers with whom they're very satisfied. Others may have needs which other competitors are better-placed to satisfy. Still, others may love your products, but not have the budget to buy them.
It's no surprise Unbounce is near the top of this list -- they've actually written the book on creating high-converting landing pages. Although there are lots of amazing things about this landing page, the two that I absolutely love are: 1) The use of a chat window instead of a classic form, and 2) the detailed -- but well packaged -- information below the form.
Full disclosure: IMPACT is a HubSpot partner -- but that's not why they're included here. IMPACT's landing pages have long been a source of design inspiration. I love the simple layout of the page, from the large headline copy and detailed featured image, to the outline that surrounds the form, to the colors and fonts that are very pleasing to the eye.
Marketing experts recommend websites remove the navigation menu and limit internal and external links on the page. The form length mirrors the value of the offer[clarification needed]. They may also include a relevant image, animation or short video. These pages also tend to contain small icons (i.e. of Facebook, or Twitter) to facilitate social media sharing.