American Society of Landscape Architects has an excellent introductory presentation here. From there you can find links to all USA university landscape architecture programs and landscape architecture offices throughout the USA.
International Federation of Landscape Architects online is here. The European Region IFLA office is in Brussels, on Avenue Louise 149/24, 12th floor.
European Council of Landscape Architecture schools online is here.
In the UK, the online presence of the Landscape Institute is here.
There are many larger landscape architecture offices which have offices and do work internationally. One of the most committed to youth is EDSA and they are online here.