The topic I'm looking for usually. I try different endings and so on until I come across one that is fairly easy to remember and sounds catchy. You just have to brainstorm a little and see what you can come up with.
Best way to come up with a good name is to do some initial brainstorming on the sorts of words you want to use. What keywords do you actually want to use in the domain? Are the words short or long? Easy to misspell?
Then take yourself over to DomainsBot for some more brainstorming. This is a great name suggestion tool. You might have used similar tools and found them to be lacking, but DomainsBot has the largest number of words and learns intuitively from what you put in. You can add your own synonyms, rank suggested synonyms, search by extension, you name it.
I can't recommend name suggestion enough as a domain name brainstorming tool. I use it constantly when creating company and brand names since there's no point in choosing a name for either if the .com domain is taken.