i would vote for prague and put budapest on your list. i didn't think vienna was all that great but i don't think i really gave it a fair chance..also, i hear some places in poland are cool, tho i've only been to krakow for a day (which was very cool).
My mom went to Vienna (a long time ago!!) and LOVED the Sound of Music tour. You get to see where it was filmed and the hills and churches used in it!! She probably has more advice, so you should e-mail her!! I remember the pictures were beautiful!!
When Wayne, Grandma Buck, my Mom and I went to Germany, my Mom and i took a trip to Graz to visit our exchange student. We spend a few days touring Vienna -- very interesting and beautiful (including the tour that Karen talked about!). The chocolate was fantastic! Have fun! :)
I heard Spain is ham-alicious. If you have a deficit in your ham levels, go there.