The best site for Bulgarian Property is EuroPropertyMap. For land plots and apartments in Montenegro click on montenegro property. There are also many tempting residences in croatia.
The real estate market in Serbia is picking up, and foreign investors are becoming more aware of the market potential in this relatively unmarketed country. In fact, compared to it's neighbour and former partner, Montenegro, Serbia is still relatively unknown.
Much of this can be attributed to it lacking a coastline, but it would be a pity to rule it out, since it's real property interest lies in Belgrade
The property market in Belgrade is liquid, with the area fetching the highest prices being Vracar, the Stari Grad (old city).