http://www.newvegasnexus.com/downloads/file.php?id=35770
Adds a custom .308, .50 and 10mm smg with weapon mods in a chest. You can get it straight out of the tutorial with 2-3 stealth boys. The scope on the .308 takes some getting used to, but they're nice.
Spoiler The box is in Quarry Junction, in the little external cave where the Deathclaw eggs are.
http://www.newvegasnexus.com/downloads/file.php?id=37060
Lets you control scope zoom with your scroll wheel. Works on Binoculars too.
http://www.newvegasnexus.com/downloads/file.php?id=34683
The Recon (Light Armor) version is great for snipers. You can pick to have all the equipment added to Docs house in Goodsprings when you install the FOMOD if you want, otherwise you have to find it all. The nightvision, thermal vision and TAC (spotter + target perk combined) modules are pretty great as well.
*edit*
Forgot one, it's pretty strong though. The lack of ammo helps keep it in check.
http://www.newvegasnexus.com/downloads/file.php?id=35484
This thing is a one handed deathfest. Uses .45-70 ammo, which is scarce. You can get it (there's only one) in Goodsprings and rebuild it at the workbench there. Has only one mod, a scope, but really that's all it needs.