I've been doing some mentalism lately, and the first port of call is Annemann's Practical Mental Magic.
In the first few pages, there's some GREAT work on billet switches, and I enjoyed learning some of the techniques. Here's how I pieced them together to make a strong routine (and get around some of the problems of using a switch rather than a peek).
Get an attractive empty glass bottle, and fold several slips of paper, tucking them inside. With the bottle, you also need a few billets and a folded dummy slip, and a pen.
To perform, set the bottle down, and bring out the billets. Hand one out, and as you return the others to your pocket, secure the dummy in finger palm. Remove the pen at the same time, and hand it to the spectator. Have him or her write any question that they like on the paper, and then fold it into four.
Take the paper back, and explain that you want them to hold the paper up to their head, visualise their question, as vividly as they can, and then pop the paper into the bottle.
During a demonstration of this, you switch the spectators question for your dummy billet. Hand them the dummy and let them hold it up to their head, before pushing it into your bottle.
With the real question palmed, put your hand back into your pocket containing the billets, and open it up (using the 'umbrella' move) and then bring out all the billets, with the question being on the face of the stack.
Remove a billet from the back of the stack, reading the question in front of you, and then return the rest to your pocket.
Take the pen from your spectator, and now give it the 'woo-woo', writing an answer that fits the question (but without revealing that you've seen the contents of the paper exactly) and have the spectator confirm that their question has been answered.
To reset, quietly fold the spectators real question paper into four in your pocket, and use it as the dummy for next time.
The use of the bottle makes an intriguing prop, a bottle of questions that people want answered, and also serves a purpose - it makes it impossible for the spectator to retrieve the question, so saves you having to switch anything back.