How I wish I had the time to do a four month trip of Europe. Good for you. Have a great trip.
My favs:
France:
Paris is by far my favourite big city. There are so many things to see. It's a beautiful city.
Chamonix
Germany: Munich
Hungary: Budapest. This is a must see. I thoroughly enjoyed the time we spent there.
Spain: Toledo, Barcelona
Italy: Venice
UK (my old stomping ground):
Scotland is a great place to visit. Lot's of great places. Oban, Isle of Skye, Edinburgh to name a few.
England: Liverpool (there's the homer in me!), London, Lake District
Scandinavia: Sweden and Finland
If you have the chance you should go to Morocco. I know it's in Africa but it's easily accessible from Spain. That would be a totally different experience from anything else you've encountered. Beware of the hustlers though!
Greece: Any of the islands are worth a visit. Athens is worth it just to see the major sights.
This is just off the top of my head. Late for work.....
