I got my bosses a nice Godiva Choclate gift set, similiar to this: http://www.godiva.com/product/gold-ball ... lastCat=18
and then I purchased a very nice professional thank you card from papyrus, like this: http://www.papyrusonline.com/greeting-c ... hanks.html
The card comes with in gold leaf, and has a gold leaf sticker that closes the card.
It all came out looking very nice and professional.
But depending on your bosses I've heard of alcohol, gift cards, high quality pen, desk clock, paperweight, card holder, etc...
Check out this post previously on the topic: gifts-for-recommenders-105925.html
and here: letter-of-recommendation-thank-you-gifts-92942.html
Also, you have to consider how many recommendations they made for you. I would personally recommend getting a gift ranging in price in the 30-50 dollar range for one recommendation, and 50-60 for two recommendations, and around $75-100 for anything more. Make sure the gift isn't too extravagent b/c you don't want your coworkers to think you are brown nosing. Well done on your acceptances, and good luck at whichever school you choose!
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