here's one of my favorite spots for jumpin on buildings:
go to new sheoth palace in shivering isles
then enter crucible
go down the stairs till you haveto like turn around to go down more stairs
jump of the ledge there to the top of the building across from it
btw make sure you have a moderatly good acrobatics skill before you do that because it would hurt like a Bword if you fall :(
and once your up there, jump from rooftop to rooftop! :D