The Templars were an international military order, formed during the crusades. From their formation in 1118 they grew in power and riches until their downfall in 1307, when King Philip arrested all the Templars in France.
The Templars were granted lands in Portugal in 1127, and established their headquarters in Tomar in 1169. They played an active role in fighting the Moors in Portugal, and when the Templars were dissolved, King Dinis preserved their holdings by forming the Order of Christ. See The Templars in Portugal for more detail.
For more information on the Templars, have a look at the following sites:
Mysteries of the Templars has an interesting collection of information, mainly on the downfall and subsequent semi-legendary influence of the Templars.
The Knights Templar in Britain is a nice collection including pictures of some Templar sites.
There is an interesting present-day Christian order, which considers itself to be a continuation of the original Templar order:
"The Sovereign and Military Order of the Temple of Jerusalem dates, in its present form, from 1804, when it announced itself publicly and was officially acknowledged by various other institutions. It claims a much older pedigree, however. According to its own assertions, Jacques de Molay, last Grand Master of the Templars, left, on his execution in 1314, a charter designating his successor. Although officially dissolved by the Papacy, the Templars, acting on this charter, are said to have perpetuated themselves through the centuries. The authenticity of the charter remains a source of contention among historians, though there is a certain body of evidence in its favor. The issue has never been one of pressing importance because the Sovereign and Military Order has never made any explicit bid for power of any kind, never has actively endeavored to wrest back the prerogatives, privileges and holdings of the Knights it claims as its predecessors. Today, it is devoted largely to antiquarian research and charitable works." THE MESSIANIC LEGACY, by Michael Baigent, Richard Leigh and Henry Lincoln published in New York by Henry Holt and Company, Inc. (Pages 353 - 361)
The Sovereign and Military Order of the Temple of Jerusalem (SMOTJ) has a considerable presence on the web: