Isner, Blake, Robredo, Almugro, Simon, etc
Blake has 2 TMS finals and big wins over Nadal, Isner beat Federer in a best of 5 away from home and beat Djokovic in IW, Simon has wins over all the top 4.
Almagro is a contender perhaps, but at least he has more clay court successes and slam QFs.
I hate Boredo more than anyone but he reached #5, a TMC and won a TMS.
Monaco's results are the weakest of all six.