If anyone's interested, here's my itinerary and thoughts on the places I went last year:
Lille - pleasant but dull, no other travellers (only stayed there for a night as the train from Paris to Amsterdam is really expensive and Brussels was full!)
Amsterdam - incredible city, nightlife and general atmosphere/cafes are great, and the art galleries are amazing and really cheap if you're into that sort of thing! On the other hand, it's quite expensive and touristy, and some of the hostels are over 18s only - so I ended up in the official youth hostel, which was fine but pricey, a bit institutional and full of school groups.
Berlin - possibly my favourite city of my whole trip! The hostel I was at was amazing, annoyingly I can't remember the name of it right now but I'll post it on here when I do. Incredible edgy, arty, bohemian feel, especially in the east around Warschauer Strasse. The lesser-known sights are better in my opinion - I've got really interested in the history of East Germany through studying it at school, so I went to the DDR Museum in the centre, which is really informative but fun and accessible, and got the tram out to the old Stasi political prison at Hohenschonhausen, which was a really interesting if harrowing experience. Tours in English only happen once a week though!
Prague - Beautiful if a little touristy, cheap and a really good introduction to Eastern Europe. Not so much in the way of big sights but the general atmosphere and architecture is really good, and for the evenings there's excellent cheap beer and good nightlife!
Vienna - spent a day there before catching a night train, would like to spend more time there!
Rome - Incredible city, the main sights are cheap or free and unforgettable! It's really easy to get off the tourist trail, just walking around is the best way to enjoy it as there's something interesting round every corner. The food from the backstreet pizzerias and restaurants is amazing and affordable on a budget - go for the places with really short, Italian-only menus, and avoid anywhere on a main square, in sight of a tourist attraction or with multilingual signs and photos of the food! The only downside for me was the accommodation - the hostel everyone seems to recommend, Alessandro's, was full, so I ended up in this really hot, cramped place spread over two floors of a dusty apartment block, with surly staff who spoke almost no English, no bar or social area, and where the heavily advertised "free pasta every night" turned out to come out of a packet!