1. Check to see if other extensions registered

The first thing I do is use Valuate.com or Estibot to see at a glance if other extensions have been registered.  I then see if the extensions have live sites and try to determine if the owners are domainers or end users.

2. Look at current Adwords advertisers for the keyword.

3. Try to determine the identity of the person contacting me.
I’ll write a detailed post on this shortly, but for starters I Google the person’s name, e-mail address, phone number and sometimes hostname or IP address.  I then compare this info to my notes from step #1 and #2 and see if I find a match.

4. Check parking/adsense stats
If the name is currently parked, I review the traffic and earning figures for the last year.  I also run a separate report for the last 30 days to see if there has been a current spike in interest.

5. Check Google keyword tool / Google Trends
Demand and cost per click can change, so I always like to take a fresh look at the current search demand and CPC for keywords which make up the name.

6. Do a Google news search for the keywords to see if there are any new developments making the domain more valuable.

7. Check for comparable domain sales
There are a number of different tools out there – I like Namebio.