Department stores and shopping malls can be found in Havana [1]. These, and smaller outlets in every town, sell Western goods from toiletries, Levis, and Reeboks to Chinese toys and Japanese electronics sold for CUC at vastly inflated prices.
If you see something you want, buy it! If you dally, it most likely will disappear. Most stores selling to tourists accept foreign credit cards except those issued by U.S. banks. Peso stores are meagerly stocked with crap no one will ever buy.
Shipping from Cuba is problematic. If you can afford it, use an express courier such as DHL (www.dhl.com [2]), rather than Cubapost (Calle P #108, Vedado, tel. 07/836-9790) or Cubapacks (Calle 22 #4115, e/ 41 y 47, Miramar, tel. 07/204-2742).
Note: U.S. residents are not allowed to bring back or mail any item from Cuba, except art and literature.
Links:
[1] http://www.moon.com/destinations/cuba/havana
[2] http://www.dhl.com