Ok, the title of this post sounds a bit Digg-ish, but honestly, DomainsBot is truly the best domain name search service I have ever seen. Let me explain why I think that.
Let's say you want to start a site dealing with Linux software, and you want the domain to be keyword rich. So you type in the phrase [linux software] and click Search. You'll get a nice long list of domains with various .tld's, and in various states of availability. You can then start whittling down the choices by creating some filters. Filter out some of the .tld's for example, and narrow down the synonyms presented. Ask it to only show Available domains, rather than expired or domains for sale. Decide if you want domains with hyphens, numbers, or bad words or not. Each choice is a simple matter of checking or unchecking checkboxes and updating the results. I've seen some outstanding domains pop up that I would never have thought of. I've taken some screenshots (below) to show you what I mean.
So, there's your keyword-rich domain tip of the day.