Tignes - Hintertux - Stelvio Pass - Zermatt/Cervinia
There are many glaciers in Europe which provide Summer skiing. The areas above are among the biggest and best.
The least known to British skiers, because it's only open in the Summer months, is the skiing at Stelvio. This lies close to the Italian/Austrian border near to Bormio and Sulden.
The area is famed for its instruction. When I last went there, several years ago, we stayed in a hotel at the base of the ski area, at 10,000 ft, and had lessons all day. Each week culminated in a race, which was taken quite seriously by both clients and instructors. Anyone looking to make a breakthrough in their skiing could do well to look for it at Stelvio Pass.
The other three areas above are all quite extensive, with Tignes and Hintertux providing quite a good variety of skiing when conditions are right. I've skied at Hintertux in June, August and October and had powder each time. October was best, though, as the temperatures were low enough to prevent the surface turning to heavy slush.