hey brian,
of course, i can recommend you many other places in central and eastern europe. i will write a short list of the cities i enjoyed the most in my travels. (in capital letters, my favourite places)
poland: wroclaw, TORUN, poznan, gdansk, hel, WARSZAWA, kraków, bialowieza national park.
czech republic: PRAHA, brno, OLOMOUC, ceske budejovice, CESKY KRUMLOV.
hungary: BUDAPEST, EGER, pest, debrecen.
romania: ORADEA, timisoara, CLUJ, SIBIU, BRASOV, bucharest, (maramures area) iasi -i havent been to iasi but i heard is veeeery nice.
slovakia: BRATISLAVA, BARDEJOV, kosice.
croatia: pula, zagreb, ZADAR, SPLIT, DUBROVNIK, osijek, PLITVICE LAKES, SIBENIK, trogir, primosten. i dont know the islands very well ... but i heard hvar and korcula are very nice.
slovenia: LJUBLJIANA, MARIBOR, ptuj, KRANJSKA GORA ... if you love big mountains!
estonia: TALLIN, tartu.
latvia: RIGA, kuuuldiga - the widest water fall in europe.
lithuania: VILNIUS, klaipeda, NERIJA - amazing peninsula...rent a bike and swin naked in lonely beaches... very advisable.
thats all my friend. i only wrote about the countries ive been to... not about bulgaria or serbia or others i dont know... so its first hand information. i wish you enjoy that corner of europe as much as i do. good luck
toni tobarra
barcelona - spain