For freeware Mike Stones C-130 is the best out there though I like a bit more detail.
If you dont mind spending a few bucks, Alphasim has a decent one at $14.00 for the base pack, and if you want a little more $14.00 additional dollars for the add-on pack. Plus they include a great sound package with it.
Now, patience is key and if you dont mind spending even more money, Captain Sim will release I would guess the MOST detailed C-130 one can imagine. Its been in the works for a while, and I have read that a release date might be after the first of the year. When? Who knows. Its development has been pushed back for a few months for company reasons...something about losing a developer because of an expired visa if I remember correctly. *shrug*
All I know, is it is one of my most anticipated arrivals to my hanger and Im getting antsy

Here is a link to the screenshots:
[link=http://www.captainsim.com/c130_hercules/]
CaptainSim C-130 Hercules[/link]
I have both Alphasim packages, but this is the one I am waiting for