Grenades

All grenades can be thrown or attached to a wall for proximity detonation. Thankfully, the grenade is smart enough to not detonate when you pass by it. Additionally, any grenade can be set off by shooting it whether planted by you or not. (Thanks Robert) Pictured above are the LAM (explosive), gas, EMP, and scramble grenades.

       
Weapon Mods

Pictured above are mods for accuracy, bigger clip, laser guide, faster reload, scope, recoil, range, and silencer. Everything is fairly self-explanatory though its worth noting that the laser guide, when enabled, gives you near perfect shooting even when you lack skill and have not taken time to aim. Combine this with a maxed out targeting aug and you'll have no excuse for not making those headshots. (Thanks brendan)

Fire Extinguisher

If you just can't find anything else, a fire exitinguisher can be used as a weapon. Think of it as a longer range pepper spray except that if you run foward while using it you will take damage. Like the pepper spray you can get around a single security beam by spraying it near the point where it contacts the wall. You can also put yourself out should you be on fire. Frankly, the one shot use and the one inventory slot per extinguisher doesn't make this very useful item to carry around.