All the places
AlphaFrog mentioned are great, and I want to add a few more to the list. Some of my favorite spots are Munich, Germany (German people have always been nice to me, and there are lots of places to go in and around the city); Lucern, Switzerland (check out the bridge over the river in the middle of the city); Amsterdam, the Netherlands (wow, what a beautiful place! You've got to take a ride down some of the canals); and Ireland, which is just nice in general.
Paris is great because there's so much to do, it would keep you occupied for years...but, as someone mentioned, it's also pretty dirty, and the people there can be not-so-nice. You'd better speak French if you want them to act civilly.
Italy is great, too, but it may be hard to get around if you don't speak Italian or Spanish, since most of the people I ran into didn't speak English. That's not necessarily bad; it just made things a little difficult sometimes. But it's a really gorgeous country.
I hope you have an awesome time!
