A really nice site with several lattice structures indexed by several methods, and new structures are continuously being added. I find it useful for getting images for problems sets and exams.
Mostly, I use the site to download "see the structure from several perspectives" images for exams and/or problem sets. I, personally, have used the Jmol renderings in Firefox (make sure Java is actually enabled, sometimes Firefox disables it as an "unstable" add-on). To date, I have mostly used the simpler structures, but there are many unique and interesting structures. One of my favorites is the half-Heusler structure. Below the links to the visualizations of the structures, there is information about how the structure is related to other similar structures. I have not recommended students visit the site yet, but I plan to in future semesters.