Great, welcome! What kind of activities do you have in mind? Exploring the history, touring tiny hilltop walled towns while tasting wine and olive oil, sailing/widsurfing, rafting, mountaineering, clubbing on a beach, or perhaps just lazing in the sun? Of course, we are a little country, so you can easily do it all (and let's not forget food and drink)

If you visit only one place, I would concur with John's recommendation: Dubrovnik it is. But there are good things to be said for Hvar, Korcula, Mljet, Rab, Istra, Plitvice, Zagorje, Medimurje... I'll try to prepare a little 'guide'...

Edit: Needless to say, if you pass through Zagreb, at least a meal is on me

Edit: removed non-Latin1 characters from toponyms