@bmo88: I spent one month in Europe (France, Belgium, Netherlands, Germany, Switzerland, Spain) in 2008. I went with a friend, and we stayed in hostels. We ate on the cheap, meaning we ate a lot of baguettes and fruit with the odd supper out. We also had a Eurail pass.
We flew from Montreal to Paris for around $800 return each (arriving in Paris was the cheapest for us). The Eurail pass I think was just over 500 euros at the time.
I think I spent just under $6000 for the month, and that included flights, train pass, accomodations, food, activities, etc. It also included clothes and my backpack, which I still have. Now we did this on the cheap though.
The Eurail pass was great. Just be aware that smaller rail lines are not included. We found that out the hard way in Switzerland when we were on the train and realized after that we had to pay for it. We just booked our rides about a week in advance (we winged the trip for the most part).
Check out hostelworld.com for good reviews. We used this site extensively when booking and it worked out quite well.
As for your cities, I really loved Barcelona and Valencia in Spain, and Berlin in Germany. Spain had a cool vibe (and lots of candy stores!). Barcelona had lots of cool architecture. Berlin had lots of history, which I enjoyed. Be on the lookout for the free walking tours. We did them in Berlin, Munich, and Amsterdam. You’ll go on an hour or so tour with a knowledgeable guide with a fun personality. They also have paid tours which they’ll tell you about during the free tour (we did a red-light district tour in Amsterdam). They’re definitely interesting and help you get a feel for what you might like to check out further.
I would just suggest that you determine what kind of trip you’re looking for – a more relaxing one or a more intense one. We did six countries in the month-long trip and we changed cities generally every 2-3 days. It was jam-packed with activities, which was fine and we got used to it. BUT, you should factor in all the time you will spend packing and repacking your bags, travelling to the train station, waiting for the train, travelling on the train, etc. It does add up. So, if you’re thinking of a more relaxing trip I would suggest cutting down on what cities you would like to visit.