A Mark VIII fan is thinner and more powerful, but won't cover the radiator as well. It also uses a two speed motor rather than the external PWM module on your stock '03-'05 fan (You may be able to use the PWM module from your old fan assembly on the HIGH input to the mark fan (or any other fan for that matter), but I don't know if the higher current draw will cause any issues)
The 3.8 Taurus/Conti fan is even smaller but flows less than Mark VIII fan. It uses the same motor and fan blade design but 16" vs 18"
The '98-'02 Continentals have a nice high-flowing dual electric fan assembly that is also lower profile compared to the panther fan assembly. These may be a better fit for the '03-'05 panther radiator.
None of the low-profile aftermarket fans from Flex-a-lite or Spal flow near as much CFM as the stock '03-'05 panther fan, and it would be dumb to sacrifice cooling efficiency for space!