@Kassem: I've been actually thinking of doing this city-hop trip when I can take a 10-day vacation:
Dusseldorf - Munich - Vienna - Prague - Dresden - Berlin - Leipzig - Dusseldorf:
(Map courtesy of A&O Hostels website)
The reason I chose these cities is that you can simply walk about and look at all the historic buildings and landmarks (and stumble upon a few of street performers, musicians and artists alike) and visit museums (which I like to visit since I'm a bit fond of European history especially regarding World War II). Also, Berlin and Dresden have botanical gardens (don't know about the rest of the cities since I didn't complete my search yet), and Dresden offers a boat ride across the river (includes lunch).
A flight from Beirut to Dusseldorf with Pegasus (on an off season) would cost around 600$ for a
round-trip ticket. Using the
ICE train, you can move between the major cities at low costs (between 25$ and 50$, less from Leipzig to Dusseldorf and from Dresden to Leipzig), so that would mount to around 300$. For residence, you can book at the
A&O hostel. I've already stayed at this hostel and it is perfect since it has branches right next to the train stations (ideal for refreshing supplies, having a quick bite for low prices like at NordSee, and of course cut down on expenses by simply walking to and from the hostel when finishing your city tour or to take the train to the next city) and offers free breakfast tokens (which I might add has a wide variety of choices and is tasty, and I highly recommend their bread). The prices average at 40$ per person if you stay alone and of course price goes down when you book per group. So that's 360$ for 9 nights.
This brings us to a total of 1260$ for major travel expenses and breakfast. If you don't spend more than 20$ per day on lunch and quick bites (15 euros), that would sum up to 200$ leaving us at a major total of 1460$. So for a budget of 2500$ to 3000$, you're left with 1040$ to 1540$ to spend on entrance fess if any (museums, gardens, exhibition centers...), shopping and unpredicted expenses.
I also recommend that you travel with a group of best friends since it would be much more fun to share the experience as well as cut down on expenses.