1 arc sec dem now available for free! This is much better than the 3arc sec SRTM but be advised there are still holes that may need filling. Format is a Geo-tiff which L3DT is capable of handling, only issue is if you output to an image file the projection can be non-squarish depending upon where on the globe it is pulled from. You have to register and go through the a process to get the regions you want, but it is worth the effort if attempting to model real world data.
http://asterweb.jpl.nasa.gov/gdem.asp