Pure tanks? According to my favorite reference, the Encyclopedia of German Tanks of World War II (http://www.amazon.com/exec/obidos/tg/detail/-/1854095188/qid=1085598948/sr=1-1/ref=sr_1_1/102-0729037-1888921?v=glance&s=books)
there are seven major tank types, Panzers I through VI, plus the Pz 35 and 38. (The King Tiger and Tiger IIs were part of the Panzer VI family).
Each of these tank types has several models (the Panzer IV, for example, had over 13 version if you inlude the first prototype and the command variants), and their basic chassis is also reused in several configurations, such as the assault guns and self-propelled howitzers, and each of these also have a few models.
The US also had quite a few tanks in WWII, such as the M1, the M2 light tank, the M2 medium tank, the M3 Light tank (Stuart), the M3 medium tank (Lee/Grant), the ubiquitous M4 Sherman and it's many variants, the M26 Pershing and the M24 Chaffee. The US also designed several others during the WWII period, but many of them never went into service.
The British armor situation was similar. They had the Matildas, Cruisers, Valentines, Churchill, Cromwell and the Firefly, a Sherman variant.
Here's another good WWII German Armor site, if you want to read up more on it.
http://www.achtungpanzer.com/panzer.htm
Nat