Sometimes I won't pick up her gift until the day before Christmas and that way she can't find it.
One year I actually bought her present and set it on top of the entertainment center in the living room unwrapped and she never found it because it was in plain site.
She has the uncanny sense that she can tell what she is getting before she opens it, so it really is hard to find her something she can't guess. I bought her a Sapphire and Diamond ring she had been looking at, and put it in the pocket of a plain cheap shirt wrapped it in a small box and then progressively increased the size of the boxes, I had a total of 6 boxes,when she finally got to the shirt,of course, she was disappointed until I finally told her to check the pocket and then she found the ring.
Another way is to wrap the present and put someone else's name on it,(say your daughter) and when the first wrapping is removed the real present is inside with your wifes name on it. It takes a little cooperation with whomever s name is on the outside package but it works once at least.
Another way to have fun with it is to hide clues, you put the first clue in an envelope with her name on it,when she opens that the clue will lead her somewhere else and there is another clue and so on till you finally give her the location of the gift. I have used this in conjunction with the double package above and that worked well.
After 41 Christmas's together I have tried them all.
madspec