For generic names, the Adwords Keyword tool is your friend:
- Look at exact match for the word(s) - this tells you how many people search for just that phrase.
- Look at phrase match - this tells you the search volume on related terms and how many related terms there are. More is good.
- Look at advertiser volume - advertisers compete for lucrative keywords.
- Look at the avg bid price - how much is it worth to them?
Use your head too - is the phrase commercial? Who would want it and why? Would it produce qualified leads or sales? What would these leads/sales be worth to them? What does that industry typically spend on technology? What does the industry spend on advertising?
Is it gramatically correct in whatever language it is? Is the word order natural? If not, don't expect an end user to build a business on it!
Also, have similar names sold and for how much? How is your name different from the ones that have sold well? Longer? Extra words? Numbers/hyphens? Different extension? For certain domains, just adding one letter like an "s" can totally kill it.
For "brandables", it's a crapshoot. Maybe someone who specializes in them has more scientific advice, but best I can say is go with your gut, if it sounds good to you hopefully it sounds good to someone else too!