PickyDomains.com is a crowd-sourced domain name suggestion service. $50 for a bunch of suggestions, you only pay if you decide to use one.
LeanDomainSearch.com is the successor to Domain Pigeon. You enter a keyword, it pairs it with 1000 other keywords and tells you which .coms are available.
Dotomator.com is a nice word beginning / ending combinator.
Dombuddy.com/generator is another beginning / ending / wordlist combinator, and also has a random syllable domain name generator.
Wordoid.com is great for syllable-connected domains that "sound" English (or another chosen language), but that also contain a keyword you specify.
Stylate is an interesting domain seller. They sell domains paired with logos for $250 - it's just enough of a value-add through curation of domains with potential and visual inspiration that I don't write them off as domain hoarders. Namella and Launchkite are competitors.
Namestation is a recent tool that combines some of the best of automated-inspiration tools with public domain-suggestion contests.
Bustaname is an awesome service for linking together keywords and generating random domain names.
If you feel that most of the good names are taken,
Launchkite.com is a directory listing of a bunch of awesome "pre-branded web 2.0" domain names. I paid $250 for a domain name and a logo for my startup, not a bad deal, and I got a pretty good name. If you're in the market, I'd recommended browsing what they have to offer. Sometimes you can find something better than those naming services can come up with.
I tried http://www.wordoid.com/ when I was looking for a name. Although I ended up not using their suggestions, the site sure helps. I would also recommend checking for domain names with prefix "the" for the name you are thinking. For example our product name is Formspider but the domain name was taken. So we went with theformspider.com.