Are you trying to pick a domain name? or choosing keywords to litter through your site? A great way to see which words are searched for the most are Keyword tools.

A keyword tool helps you find the best keyword. For example using "motel" when you should be using "hotel". These tools are really straight forward to use, you put in the word you think you want to rank well for, the tool generates the most searched terms related to your keyword.

I have found the following keyword tools, but I mostly just use Google's.

I'm not a keyword expert (I think it's really spammy) but I do take into consideration the keyword tool results when purchasing a domain. If you would like to learn more about keyword tools, browse the references below.