(I have already seen some of these before during my childhood)
1. Top on the list is the Phoolon-wala baazar (the flower market) at CP: Obviously one has to be up before dawn to enjoy it in its full glory
2. Humayun tomb
3. Safdarjung tomb
4. Akshardham mandir
and then there are several unexplored heritage buildings that I have seen from a distance but never visited...
and, then there are numerous restaurants and pubs on my 'to do' list!