Here are a couple useful mods I find make World of Tanks either easier or more enjoyable to play. All of these mods I am currently using.
J1mb0’s Crosshair Mod:
Very clean crosshair mod that has a reload timer. I like this since it is simple and easy to see where you are aiming.
Max Visibility Mod:
This one is somewhat newer and right now the only main post about it is in Russian. Essentially it removes the fog and improves FPS. It boosted my fps by 15-20 in most situations and actually improves the look of the game. Keep in mind that this will only improve the FPS if you have a decent computer and if you have an older/slower computer it will actually have the negative effect and drop your FPS.
Link for US English topic: Inlcuded here is the link for the download and/or author’s thread that is in Russian.