I don't know how long you have to travel, but I am working on an itinerary for a 5-6 month venture through Europe starting in August 2005. (yeah quite a distance, but have to pay off debts). Anyways for sake of not making it too long I am leaving out most cities.
Arriving in Amsterdam, Netherlands
to Sweeden, Norway, then hopefully up around the coast and down into Finland.
From Helsinki arrange for a group tour to St. Petersburg, Russia.
Upon the return from Russia take the ferry down to Rostock, Germany.
Make it down to Munich for Oktoberfest
, then travel the rest of the country to see relics of WWII, etc.
Head back to Netherlands and Belgium.
Over to Paris, France, and travel through Lyon to Madrid, Spain and Toledo. Head over to Lisbon for a couple days
Swing down to Seville, Gibraltar and up to Barcelona.
Stop by Nice/ Morocco on my way to Milan, Venice, Florence, Rome, Naples and Palermo in Italy.
From the port of Brindisi, Italy catch a boat to Patras, Greece and visit Athens and Cyprus (although due to a recommendation earlier Crete may be added) :P
Back to Athens, head up to Vienna, Austra and around the country then back to Prague.
Leave Prague to see Warsaw and then Budapest in Hungary.
Go back to Vienna and head over to Switzerland for a quick tour.
Split from there to London through Paris.
Spend Christmas in York with family, then back to London for New Years.
Venture my way across England to Liverpool to hitch a ride to Ireland and then back to Scotland.
Then take the last of my free train rides back to London and hang out till I feel like flying back to Detroit. (actually when I have no money left and have to fly back)