I want points for practicing triangulation algorithms.
Just points with coordinates [X,Y] and elevation [Z] of real world terrain.
I can use Google Maps Elevation API, but there is no method how to get only significantly terrain points.
I provide a number of sample LiDAR files at http://liblas.org/samples that you can download. These are mostly example data, but many are quite interesting. You can use the las2txt utility that libLAS provides (or Isenburg's las2txt version as well) to convert them to XYZ ascii files.
Isenburg's tools also provide a number of fantastic triangulation algorithms that anyone looking to manipulate and work with high-throughput LiDAR-derived elevation data should have working knowledge about.
One option is using the sample *.las files on this site: http://www.cs.unc.edu/~isenburg/lastools/ The site also contains tools to convert them to xyz text files.