I've tried a few free apps over the past few months, but have just found the Galaxy tarot app which seems to have much more potential than the others. I'll have to see how the readings feel over time, but I like the availablilty of symbols, numbers, suit links. The card meanings are listed from a variety of people/sites giving a rounded feel.
I also have and like the Osho Zen app which is very different from the Rider-Waite or Thoth systems. Gives a totally new, fresh face and different perspective.
Enjoy, and happy holidays.