Season 5 of Stargate Atlantis was the last series. Stargate Universe will replace it in the near future with Actor Robert Carlyle taking the lead role.
Like all great series, eventually they run out of energy and have to make way for new concepts. I suspect that like Startrek generations, Stargate and Stargate Atlantis will go on forever simply because they represent brilliant story telling and push the boundaries of the imagination. Strangely these Sci-Fi series have a way of creating their own virtual world that draws you in.
There is some excellent TV shows at the moment (24 & Damages) that suck you into their virtual world and have the power to surprise and make you think.

Stargate Atlantis 1-5 dvd
star trek collection
http://www.dvdcollects.com