What makes some pre-launch sites great? There is a lot of talk about beginning to market your site well before launch. How does one do that on a "coming soon" page?
Most of the pages I've seen just have a logo, maybe a product shot, a one liner description and an email box to be notified when it launches.
Are there other things I should consider adding?
There are some things that can make your pre-launch site great, but let's consider first what its main purpose is. The best possible scenario is that your promo content goes viral and highly shareable.
Write the detailed description: features of your product, what value it brings to potential users.
Add more screenshots and pictures of your product.
Add videos which show how to use your product. If it's possible, use content marketing, create "how-to" videos and answer the questions, explain to people how your product may solve their problem. YouTube can do really good in terms of creating shareable content. Make sure that your videos are attractive and really bring value to users, no one enjoys watching dull self-promotional videos.
Engage website visitors: Offer discounts, privileges etc. in return for pre-order or subscription.
After-email surveys or calls to action. Don't have it visible beforehand, because you need to keep these kinds of pages focused, but you can get more value out of a visitor after they've submitted their email by either prompting them to fill out a brief survey (helping you understand who they are / why they're interested), or to follow you on social media, helping you build an audience you can leverage for even more pre-launch interest.
Contact info. Enable serendipity by making sure you have an email address visible. Customers, partners, press, even investors may want to reach out if what you're doing sounds valuable to them.