The Egyptian museum
The current Egyptian museum is in shockingly bad condition, considering the importance of some of the exhibits (the tomb of Tutankhamun, for example). Apparently a new facility is being built and will be ready in 2011; until then they have stopped putting money into the old one, and sadly it's in quite a state of disrepair. Entrance costs €6, and though the building itself is terrible, the exhibits are fantastic. I could have walked around for days, but as we only had a couple of hours our tour guide concentrated on the most important pieces, some of which are several millennia old. I think it will be fantastic once they move everything over to the new facility - I'll be sure to visit again then.