When it comes to designing coming soon webpages you want to make sure that you have something up on the domian that looks professional but also do not want to spend too much time and money on something that will be replaced.

Smashing magazine have an article looking at various coming soon pages with some good examples. One thing that you may want to consider is having a signup for more information form, also a brief description about what is coming soon.

The points are:

1) Tell us what to expect.

2) Provide updates (email signup)

3) Create some intrguige

4) Rembmer SEO

Read the article:

http://www.smashingmagazine.com/2009/11/10/designing-coming-soon-pages/