The bus service in Croatia is first class: there is even a bus connection between the smallest villages in the country. There are express buses that cover longer distances and which are reasonably comfortable. Bus travel is also inexpensive, and the new motorways in parts of the country have reduced journey times considerably.

In almost every larger town, there is a bus station (Autobusna Stanica) where tickets are sold and timetables are clearly displayed.

Bus Companies in Croatia
Please see the following websites for timetable and price details. (Unfortunately, some of these websites are in Croatian only!)

AK Karlovac
APP Variety of domestic routes
Autopoduzece Imotski Routes between main cities
Autotrans Rijeka based company
Brioni Pula based company
Cazmatrans
Croatia Bus Zagreb based company
Contus Services between Zadar and Zagreb
Panturist Routes from Osijek to Zagreb and the coast
Promet Makarska Routes from Makarska down the coast and to Zagreb
Promet Split Routes in and around Split
Samoborcek Routes between Zagreb and Split

Bus Terminals in Croatia
Timetables can also be found at the following websites.

Dubrovnik Bus Terminal
Split Bus Terminal
Varazdin Bus Terminal
Zadar Bus Terminal
Zagreb Bus Terminal

Autobusni Kolodvor is also a very useful website on which you can look up bus timetables for the whole of Croatia.