Starting from the end of November to Christmas, there are numerous Christkindlmarkt in downtown Vienna, all in different sizes. Other than the one at Rathausplatz, the plaza in between the KHM and the Museum of Ethnology also hosts a nice Christkindlmarkt, having the two museums as background. However, I didn't get the chance to photograph it. Schonbrunn Palace and Belvedere also hold their own Christkindlmarkts. The one at Schonbrunn Palace even has live band performance!
One fun thing about the Rathaus Christkindlmarkt is that they cover up the windows using fabrics each marking numbers 1~23, and the biggest window right beneath the clock is marked No. 24. The numbers are marked randomly. Each window is actually dedicated to one painting. From December 1st, one painting will be uncovered each day according to the number, and the biggest painting on the Christmas' Eve.
Another favorite of mine is the Christkindlmarkt at Karlsplatz. The baroque Karlskirche is so photogenic that it's almost perfect at every angle.
One important thing to note is that anyone who wants to come to Vienna to enjoy the Xmas atmosphere should do so before December 24th. From early afternoon of the 24th to the 26th of December, almost all shops are closed (with very limited exceptions of restaurants). The Christkindlmarkts are slowly removed since the 26th. If, unfortunately, you came to Vienna on Xmas, you should expect to face a ghost-town-ish situation...
On the 26th, all stands at the Christkindlmarkt are closed. Only the Christmas Tree is standing tall alone.