I've seen this happen for configurable and bundle products where the item was added to the wishlist from the product gallery/listing page (versus the product details page). It seems that if a product is added to the wishlist without selecting any configurable options, Magento displays the Base Price. If the Base Price is empty (or, more specifically, generated from the price for each configurable product's price) then it displays $0.00 since the product's price is dependent on the option selected. This was, at least, the scenario I had where I saw this.
However, once a configurable option is chosen, the correct price will show up in the Wishlist. As much as it appears to a customer that there are free products for them to purchase in their wishlist, they just haven't provided enough information to Magento (nor to anyone wanting to purchase something from this person's wishlist) to determine a price.
The desired functionality here should mimic what is done when trying to add a configurable product to your cart -- you would be taken to the product details page to select the configurable options and then select "Add to Cart" or, in this case, "Add to Wish List".
