wheel - 12:59 pm on Sep 23, 2010 (gmt 0)
I go with my main corporate name for branding, and that's the focus of my efforts. Use secondary websites to target secondary search terms and for secondary purposes (i.e. a blog).
As you grow, the brand name becomes more important. Long term you don't want people thinking of you as secondarysearchterm.com instead of yourcompany.com.
If you are going to use secondary domains for search terms, watch your logs, and check for availability of exact match domains. There's still plenty available.