Backstreet look at the shopping center Novy Smichov. It is probably the best "in the Prague center" shopping center in Prague :) ... considering people going to and actually shopping here. The shopping center at Flora (also a metro station) may be as popular as Novy Smichov. Chodov (also a metro station :) would follow. Novodvorska Plaza and Eden would be on the other end - they are definitely not successful. Then there are "on the outskirts" shopping centers, but I won't bother you with them.
We will have a new shopping center very close to Old Town. But not as close to ruin the historical feel of Prague. It is called Palladium and is located at Namesti Republiky square (also a metro station). Opening of Palladium will be a big event. A lot of new brands entering the Czech market will have their first shops here. Palladium is at a very lucrative place - it is just a minute from Prague's shopping street Na Prikopech. Palladium opens on October 25.
PS: Abbreviation for shopping center in Czech language is OC ("obchodni centrum"). Do you know anything else named OC? Maybe a TV serie? :)
PPS: Lindex is one of the new brands in Czech republic. Actually they opened their first shop in Brno just a week ago and will be at Palladium, too. If you are from Norway/Sweden/Finland - do you know Lindex? What do you think?