Strictly speaking, a broadsheet newspaper is any newspaper that is printed that is printed on a full-size newsprint. In countries where ISO paper sizes are used, a broadsheet is generally an A1 sheet which is folded in half to produce an A2 leaf. Tabloid newspapers are printed on newsprint that is usually half the size of a broadsheet.
The broadsheet format has evolved such that it is now generally associated with high quality newspapers, such as those listed by mgriffithsuk. However, there are still quality newspapers, such as the Australian Financial Review that are still printed on tabloid newsprint.