Hiya mate,
Xzone is definitely the biggest Czech "pure" video games seller, it isn't the cheapest one but with its special (weekend) offers and some kind of "loyalty proram" (you are recieving virtual coins when you buy something and you can u these coins as usual money when buying some game next time). JRC is also big shop, but i still prefer Xzone. Alza is biggest electronics vendor, but games there are generally more expensive and their range of games is quite limited.
I personally prefer UK shops, but sometimes I buy a piece in Xzone ^^
Edit: Talking of beer, i like Svijany maybe it's not the most famous, but i think it's da best =D