Congratulations Brew!
I think magic is right...in a way. It depends on your wife- if she's spent the last several years as a stay-at-home mom taking care of your daughter...well, she probably would love the break. However if she's really family oriented, then you might reconsider sending the daughter away.
As for ideas: are you handy with a computer? Why not take some photos, scan them, and make a collage of you together? Then frame it and present it to her. Maybe you already have lots of photos on the wall already. Why not write her a heart-felt letter to give to her over dinner?
Also, you could get a plate and a ceramic pen, and write some meaningful things on it, and get your daughter to write something like "I love you mom and dad" too! Bake it in the oven, and you have something that can be useful too.
Here's a craft board if you are creative and handy (it is actually a board for Valentine's day, but still romantic, you know?):
http://www.craftster.org/forum/index.php?board=99.0