I like mathematical magic, as long as it isn't filled with lots of adding, counting, and...well, math. In other words, I love mathematical pricinples when they don't appear to be mathematical principles. In the Big Deal, a math principle is well disguised to let you force a specific card in a very clean way.
A deck of cards is shown to be normal -- (it almost is... in fact, I had mine out and was shuffling it and using it and did not realize it was gimmicked at all. You can use it for all your other routines with a small bit of care.)
A jumbo card prediction is placed facedown in full view. The deck is placed on the table. The spectator is given five "number cards" that show 1 through 5, and she picks any two of the five cards, to create a two digit number. (Let's say she chooses the 4 and the 2, and makes them into 42, but then she changes her mind and makes them 24, and then she changes her mind, and puts back the 2 and takes the 3, and makes 34 instead -- whatever she wants, there is no forcing here). The magician picks up the deck and slowly and cleanly counts 34 cards into her hand. To "further randomize the choice", the two number card digits are added together (in this case, 4+3 = 7), and the magician counts 7 cards from the packet. The card arrived at is handed to the spectator. All the other cards are shown to be different -- the deck could even be sorted into ordered values and suits to show that all the cards are different, and only one card is missing -- the one she holds. And this card exactly matches the jumbo prediction.
The use of number cards to make the selection is a bit illogical, but it seems to give the spectator so much free choice that it also appears to be very fair. Even if someone works out the arithmetic involved (maybe a math PHd in the audience), they still will not understand how you hit a single prediction card. This is a fooler that you can use anytime.