I've been to:
England (London, Plymouth, a lot of spots in Cornwall and around the rest of Devon, Manchester)
Scotland (Edinburgh, Glasgow, Isle of Skye, Barra, various trips up into the Highlands)
Spain (L'Estartit, Barcelona)
Italy (Rome, Bologna, Florence, Bari, Sorrento, Amalfi Coast)
Greece (Athens, The Islands: Santorini, Paros, Antiparos)
Croatia (Zagreb, Split, Dubrovnik, The Islands: Hvar, Bol, and another I can't remember, drove around the Istrian Peninsula from the Slovenian border to Split, Plitvice Lakes)
Bosnia (Mostar, Sarajevo)
Romania (Bucharest, Transylvanian Alps: Brasov)
Hungary (Budapest, Sentendre, Eger)
Poland (Krakow, Zakopane, Lublin, Warsaw, Gdansk, Wroclaw)
The Netherlands (Amsterdam)
Belgium (Brussels, Brugges)
Slovenia (Ljubljana, Bled, The famous caves out towards the coast at Divaca (Skocjan Caves), Piran)
Sweden (Stockholm, Varnamo, Gotland (Visby), Jonkoping, Vaxjo, Gothenburg, Malmo, Halmstad, Boras, Granna)
Iceland (Reykjavik, Vik)
Czech Republic (Prague, Usti Nad Labem, Cesky Krumlov)
Japan (Tokyo, Osaka, Kyoto, Nara, Hiroshima, skifields, etc. Was a one year student exchange.)
My favourite...probably the Scandinavian countries. Least favourite was Bucharest...then probably Paris, but only because it was early in my travels and I don't think I made the most of it.
I'll try to find some photos for each country and post them.
A highlight from the last trip was sitting up in the castle above Piran with a mate talking rubbish and watching the sun set over the town. Behind us there was a soccer field and a local team, who we dubbed 'The Slovenian National Team', were practising. One guy knocked over all the witches hats (there were 4) while trying to dribble between them. Great fun.
I'd highly recommend going to Croatia (Plitvice Lakes are outstanding), Edinburgh, the Amalfi Coast, Bosnia, Sweden, Iceland, Denmark, Slovenia (especially Bled and the areas around it...as someone elses picture shows, it's a beautiful place...except for the big hotel or two on the lake
), Brugges, Gdansk, Zakopane & Krakow (they're near each other), Transylvanian Alps, Edinburgh & The Highlands, Isle of Skye, Cornwall, Cesky Krumlov. The Skocjan Caves are wonderful...get there by 1pm at the latest to do the tour
I'd avoid Prague in the tourist season...it's a mess and the large number of tourist groups following flags/bottles/annoying voices and narrow lanes end up pissing you off. There are also a lot of people wandering the town square these days offering drugs, sex, access to strip shows. The Central Train Station is dingy and feels very dodgy. Fortunately most trains from other countries come in at a different station but some local trips (like the train to the town that has the bone church) leave from Central Station. When I arrived back from the bone church I crossed the road from the train station and saw a lady with a baby shooting up in the park. It's no different to any other city I suppose, but it's changed quite a bit since I was there 4 years ago. Having said that, Charles Bridge is stunning in the evening/early morning and if you are lucky enough to find yourself in a laneway on your own surrounded by old buildings it's beautiful...even when you wake up 5 hours later lying on cobblestones without your wallet
Bucharest was pretty ordinary in my opinion. But then we were only there for 5 hours...the Parliament Building (or Palace) is very impressive.
Plymouth is good for a visit to the Barbican on the way to Bude or Tintagel on the Cornwall Coast. Half a day should do it...I was there for 7 months