Well, I don't want to sound like I am full of myself, but most of the stuff I will recommend is mine. :D
The really good skins by other people also have to be good if I recommend them. I have high standards.
I'll recommend a few skin-packs and a skin for each weapon.
AK-74 packThe first weapon pack I ever made :D
Eh, I'm too lazy to hyperlink each one, so I'll be lazy and just past in the links.
http://www.fpsbanana.com/skins/26460 - AKs-74u
http://www.fpsbanana.com/skins/33624 - P-99
http://www.fpsbanana.com/skins/33628 - Beretta 92FS
http://www.fpsbanana.com/skins/35565 - G-36
http://www.fpsbanana.com/skins/35761 - Vintorez
http://www.fpsbanana.com/skins/35797 - Browning HP
http://www.fpsbanana.com/skins/39307 - Groza
http://www.fpsbanana.com/skins/39797 - USP
http://www.fpsbanana.com/skins/39835 - Spas 12
http://www.fpsbanana.com/skins/26583 - LR-300
http://www.fpsbanana.com/skins/26689 - Colt 1911
http://www.fpsbanana.com/skins/41907 - L-85 and Stalker suit
http://www.fpsbanana.com/skins/41273 - AKS-74
http://www.fpsbanana.com/skins/44864 - knife
http://www.fpsbanana.com/skins/40369 - Makarov
http://www.fpsbanana.com/skins/45188 - PB silenced
http://www.fpsbanana.com/skins/40723 - Fort 12
http://www.fpsbanana.com/skins/46264 - Sig P220
http://www.fpsbanana.com/skins/46854 - Desert Eagle
http://www.fpsbanana.com/skins/46098 - MP-5
http://www.fpsbanana.com/skins/42668 - Sig-550
http://www.fpsbanana.com/skins/35580 - TOZ-34
http://www.fpsbanana.com/skins/42792 - BM-16 sawnoff
http://www.fpsbanana.com/skins/39678 - Abakan
N-gons are polygons that have more than four vertexes. Metasequoia does not support them, but other apps do.
The reason I do not like people using n-gons is because game engines break down n-gons and quads into tris, but n-gons are irregular in their disassembly. As a result they create a mess that is unorderly and often results in microscopic tris that are annoying to find and uv.