I got 45 fairly easily, but ive been writing html for a long time. Would love to see the output reveal them in a list in order of commonality - would love to see if im missing some common ones - like if you guessed 1-20 but missed 9...
<img> also took me the longest time, and <br> even longer though I used it within the last hour, but the facepalm moment came when I almost decided to give up and then remembered <h1> through <h6>. I even knew how many levels existed! Not that I didn't try h7 for good measure, one can't be too sure with these things :-)
edit: Case in point, I missed <img>...