The first two exit polls show Stjepan Mesić with a commanding lead. Puls has Mesić at 70.85% and Kosor at 29.15%, while GfK has Mesić at 71% and Kosor at 25.5%. This is more variation between sources than I would need to consider either reliable. Also, the surveys were conducted only on RH territory, not BiH.
Update: Nobody wants to cast doubt on any results, of course. But B92 is reporting a result of 70.75% for Mesić, 39.15% for Kosor. Which adds to 109.9%, an incredible turnout by any measure!
Update2: GONG's first unofficial projection: Mesić 65.62%, Kosor 32.78%. The official results will have to be announced sometime in the next few hours, but this seems beyond the capacity of fraudulent results from Hercegovina to alter. Ratko Maček, campaign director for Kosor, says they would be happy with 35%.
Update3: Final result according to the Electoral commission, as reported by Index: Mesić 65.98%, Kosor 34.02%. On the territory of Croatia, Mesić won in all districts except Ličko-senjska, 47,24% to 52,76% and Šibensko-kninska, 49,70% to 50,30%. The vote was close in Splitsko-dalmatinska, 50,85% to 49,15%, but he won by large margins everywhere else in the country. The "diaspora" vote was hugely lopsided in the other direction, though, as Quod observes in the comments: 17,47% for Mesić, 82,53% for Kosor. There are clearly major differences between voters who live in Croatia and voters who do not over where the country's interest lies.
Update4: I do believe that I agree with the people who are saying that it would be good for both Croatia and Bosnia-Hercegovina to do away with the "diaspora vote." It came into being as a manifestation of Mr Tudjman's territorial ambitions and as a way of assuring a permanent reserve of votes for HDZ, and it is now a bastion of irresponsible influence and fraud.
Update5: It looks like Mr Mesić agrees with me, imagine that. Ordinarily he might not get far in wanting to eliminate the "diaspora vote," especially with HDZ in government, but there is the added factor that the EU wants uniform electoral laws.