Germany, for example, has a (pretty complicated) voting system that insures that every constituency has one representative (that's half of the parliament, the other half has, technically speaking, no constituency but they are obviously still from somewhere).
Everyone gets two votes, one for a representative from the constituency (whoever gets the most votes wins and will definitely be in parliament), and, more importantly, a second vote which determines the proportions of the parties in parliament. (Seats that parties cannot fill with directly elected representatives are filled from the party list.)
That second vote decides about the government (proportionally!), the first makes sure that every constituency has someone in parliament they can write letters.
This voting system is called mixed member proportional representation and here is the link to its Wikipedia article: http://en.wikipedia.org/wiki/Mixed_member_proportional_repre...