Latvia: Riga (twice), Ventspils (twice), Valmiera - always one day trips, so not much to tell. Anyway I liked my time there
Estonia: Tallinn (3 times, 7 days overall) - enjoyed it more than Riga, but of course I spent much more time there. The first two times I was there it was mostly raining, but third time was much better
Poland: Krakow (two times, 2 days) - Nice city, plenty to see there, but it was only sightseeing both times, so not much to tell.
Sweden: Norkoping, Stockholm - absolutely wonderful time there! It has the most to do with Lithuania winning EC03, but when in Norkoping in September weather was very good for what I expected from Sweden and we had great parties with great people. Fantastic memories
Slovenia: Novo Mesto - small town or big village in winter... hrrr... Also we got lost in Slovenian mountains driving to the place, but generally I liked the trip (alcohol probably has everything to do with it

)
Greece: Athens (during Olympics), Argostoli and Amaliada (this summer) - Olympics was obviously a great experience as well. Lived far from the city, but near the sea, Ouzo, great people and parties again. Staying in the city after games was amazing as well, with nightlife lasting till the morning light. Argostoli in beautiful island was a nice place too. Amaliada - very dull city, but as we stayed in the best Greece hotel near the Mediterranean sea, who cared about the city
Montenegro: Podgorica and Petrovac - trip to Montenegro over the mountain roads was a killer one, but time spent there compensated everything.
Serbia: Belgrad - Nothing too fancy apart basketball. Some parties in Lithuanian bar created just for the time of EC.
Italy: Treviso and Venice - two nice cities. We lost on the way out of Venice and spent over 2 hours walking in circles, so killed the mood a bit. Anyway it was nice trip.
Also drove through Czech Republic (spent 2 nights in hotels there), Slovakia, Hungary, Bulgaria and Austria.