In most cases, a 2-word niche domain is already registered. Buying the domain isn't feasible because of the high cost. Adding prefix/postfix become a fast and low cost method. I usually go to google / amazon. use their autocompletion to get another long tail keyword. Some will use common postfix, for example, pat flynn's blog uses a postfix "hq". What words do you usually use for these prefix/postfix when registering domain names?