Wikitravel uses separate phrasebooks for Serbian, Croatian, and Bosnian, to help travelers avoid mistakes based on regional differences. The differences, in both vocabulary and accents, between one and the other are very miniscule, and any of the following phrasebooks can be used wherever you may go and get along with it.
Bosnian phrasebook - spoken in Bosnia
Croatian phrasebook - spoken in Croatia
Serbian phrasebook - spoken in Serbia