Iron Front Liberation 1944 based on the Arma engine is also fantastic for its combined arms play.

WW2 Sims
 

You basically have three to chose form:

1) Steel Fury which was made in 2007and has been greatly modded and expanded, Panzer Elite which goes back to 1999 but has been heavily modded and updated and is still played and T34 versus Tiger from 2007 which was almost sent to an early grave because it was buggy , unfinished and the developers dropping it like a hot potato. Currently only Zeewolf mods it but his mods are not free.

Steel Fury is only SP( here's the link to the forum http://graviteam.com/forum/index.php?board=1.0 )

, Panzer Elite is both SP and MP ( here's the link to their forumhttp://pedg.yuku.com/directory#.U1CdaE2KCUk)

TvsT also but nobody plays the MP anymore and for the SP you need to subscribe to Zeewolf's membership there's sticky dedicated to it a little above.

War Thunder has mixed arm battles (tanks and planes), and is much cheaper. With tanks now out, I can say as part of the CBT, they were very fun to ride in, with the added bonus of, if you are destroyed by a tank, you can hop into an IL-10 to pay him back in kind. World Of Tanks does not do this.

If you're looking for an MMO WW2 tank experience with Western Front equipment, you may wish to check out (if you've not already) ww2 Online. Its been around since June 2002 (and the graphics show it, but that its still around and people pay to play is testament of its value).

Or you can try Red Orchestra 2 Heroes of Stalingrad which has some playable tanks( Panzer IV F2, T 70, T-34/42 etc) and some maps made for tank warfare.