I've been playing courses in both Europe and the US but coming up with just a few of the best with a short motivation would leave the list as this -
1. Kingsbarns - Scotland, just outside the city of St. Andrews - I played it in early may and this course is a real beast when the wind is on. Add to it a lot of beautiful views and awesome architecture from the course designer and you have a great experience. This is the first time I've ever told myself several times "I don't have this shot in the bag, there is no way you can make this". A 78 (+6) made me real happy the day we played it. Cost was 200 british pounds but well worth every single penny.
2. St. Andrews, Old Course - Doesn't really need any kind of motivation. Sure the course is real short but the historical importance of it and just the big smile on your face cause of the simple fact that you're really there makes it one of the best courses I've ever played.
3. I can't really decide right now there are a lot of great courses up there, both in the US and in Europe. I will get back to you!