Croatian coast is very long and there are quite a lot of places where you can surf and/or even kitesurf. In the summer time, I'd recommend south part of the croation coast (Dalmatia). A few places:
Definately worth visiting. Yes, the Golden Horn will be busy during the day and it will be forbidden to kitesurf there, but just a hundered meters away there will be dedicated (and reserved) spot for kitesurf launching. Usualy, you'll get around 4bf NW wind (maestral) every day. Also, do not forget to visit two other places on island Brac: Supetar (nerby where the car ferry lands), which is a good sport for S wind (30% more power than in Bol) and and Povlja for NE wind. So you have all wind conditions covered. (Get more info on http://www.zutimacak.hr
More to the south. Great spot. Maestral wind (NW), usually around 5bf starts in the afternoon, many times, you'll also get 3bf S wind in the morning. Enough place to launch the kite, side shore wind, the spot closes to the bay (good for beginners). (I will be there fom 20th of July till at least 10th of August.)
Some other spots, more to the north:
-Umag (close to Slovenia border)and Premantura (near Pula) in Istria
-Island Krk (near towns Punat and Baska)
In general, there are many other places where you can kite. Just look around a little bit and try to find a good spot to launch a kite. Also, kitesurfing is not yet forbidden at the croatian coast IN GENERAL (and we would like to keep it this way) so please be carefull not to launch the kite in the crowded places.
Hope this helps just a little bit...