You ask the spectator to name any card (no force, completely free choice). Then while you turn your back you ask them to cut a portion of the cards off the deck.They can cut as much or as little as they want it's totally a free choice.You ask the spectator to count the cards to get a random number.
The spectator counts down to their chosen number and turns over the card,it is their freely thought of card.

Extremely easy to do
Fully impromptu 
No sleight of hand required
Almost self working
Use a borrowed deck
No memory work or crib sheets 
No gaff cards