Hmm... Free ones? There are a lot, but I usually stay away from them as I usually end up disappointed. The Zenonia series seems quite popular with people, however, and it's free (I think).
Here's a list of the RPGs I have on my iPad/iPhone:
Ash
Ash 2
FF Tactics
FF Dimensions
FF1
FF2
FF3
Bastion
Chaos Rings
Infinity Blade
Sword and Sorcery
The World Ends with You
Sadly... None of those were free
My best advice is to check sites like Appzapp.us or Appshopper daily and wait for things to go on sale or become free. You missed HUGE sales over the X-mas holidays, but they will come again if you are patient.