I wrote a while ago about using M-^ to join the current line to the previous line. In fact, when editing I find that I most often want to join a line to the following line. I used to do this by using C-e to move to the end of the line and then C-d to delete until I got the next line joined to the current one. It is easier to do this with a single key using a simple function, which I set to C-j. Add the following to your emacs config file:

;; join line to next line
(global-set-key (kbd "C-j")
            (lambda ()
                  (interactive)
                  (join-line -1)))

You can keep hitting C-j to keep joining the next line.