As far as I know plaisio (a Greek company) has presence in Roumania as well, so I would suggest looking for the Turbo-X I50 (manufactured by the company) it's unlocked and you can load various of navigation softwares (iGO, Genious Driver, Destinator etc).
Having just had a quick look at Garmin City Navigator Europe 2010.2 it appears to have pretty good coverage of both Romania and Bulgaria, so any recent Garmin GPS unit would probably do the trick. If it were me, I'd get something with an SD card slot so that I could load additional maps if necessary.
How much were you thinking of spending and do you want something that's waterproof and motorcycle friendly?