Simple and useful - Vortex 8x25mm Solo Compact Waterproof Monocular

This optic is very small and light weight making it extremely useful. It is rugged and can be carried just about anywhere you need it. There is nothing fancy about it which I think is it's biggest strength. The 8x is perfect for scanning and general observation out to about 1000 - 1500 meters. The case is not very good but it's easy to find a replacement because of the size. It can fit into a 5.56 mag pouch.