Note that some of the mods linked here may be outdated and make your game unplayable.

Mods:
Crosshair mods:
http://forum.worldoftanks.eu/index.php?/topic/56831-j1mb0s-crosshair-mod/  (Very popular)
http://forum.worldoftanks.eu/index.php?/topic/112940-vanilla-reloading-crosshairs-for-80/
http://www.skins-wot.net/load/priceli/8_istoricheskikh_pricelov_v_7_3/201-1-0-789
http://www.curse.com/wot-mods/worldoftanks/scope-shadow-remover

Damage panels:
http://forum.worldoftanks.eu/index.php?/topic/89516-damage-panel-134-int-83-centered-and-vanilla/
http://www.curse.com/wot-mods/worldoftanks/camo-rabbit-damage-panel-0-7-5

Graphix mods: (these can negatively affect your game's performance, especially if you play on a toaster)
http://worldoftanks.tv/downloads/misc/1331-fxaa-uluchshenie-grafiki.html
http://mrhaandi.blogspot.ca/p/injectsmaa.html


Misc:
XVM, mod that is supposed to tell you who is a good player and who isn't:
http://code.google.com/p/wot-xvm/downloads/list

Stat Calc, see what your tanks' effective reload/aim times/view ranges are
http://forum.worldoftanks.com/index.php?/topic/168391-wot-tank-stat-calculator-android-windows/

http://www.skins-wot.net/load/mody/minikarty_vysokogo_razreshenija_s_bazami/200-1-0-912
http://www.curse.com/wot-mods/worldoftanks/camera-mod
http://forum.worldoftanks.eu/index.php?/topic/46236-pogs-contour-icon-3x-grepa
http://forum.worldoftanks.eu/index.php?/topic/159855-080-vertical-tech-tree-with-pretty-lines/

Mod that makes the vanilla tech three more compact:
http://www.skins-wot.net/load/mody/kompaktnoe_drevo_razvitij_tankov/200-1-0-1601


Mods such as >historically accurate remodels and crew for open topped vehicles can be found here:
historicalrealism.blogspot.fr/

Miscellaneous:
German themed playlist:
http://www.youtube.com/playlist?list=PLDE8EC7367D6F745C
An outdated version of it can be found here: http://www.mediafire.com/?sbus70kqy9fuzga

Russian themed playlist:
http://www.mediafire.com/?j5bl8v0sc31uh7v

Skins made by fellow /vg/ tankers
ELC AMX:
SANIC: http://www.mediafire.com/?azbbf7rbp9adfv9
Blue Falcon: http://www.mediafire.com/?4iheh3z6kot9m39

Red Panzer Leopard and Pz2 Luchs:
http://www.mediafire.com/download.php?buu477xoet258ds
http://www.mediafire.com/download.php?buu477xoet258ds

King Tiger with some pinup on its turret side:
http://www.mediafire.com/download.php?fcd7bymfc3rzgqv

These two turn your blueberry french tanks into panzer tanks
Grey panzer skins for the entire French tech tree:
http://www.mediafire.com/?aevays11avxk0z3

German decals to replace the french ones:
http://www.mediafire.com/?k8u57geuo76zd62

German-captured type 59 skin:
http://www.mediafire.com/?w7wav2i0fgwaq96