Used for connecting batteries and ESCs, this is one of the most common types of R/C connector on the market.  This is an "improved" version of the original, it features an easy-to-grip rib molded along the back edge of both pieces.  These are made of nylon, not plastic (like the orginals), which makes them resist the heat of soldering better than many other similar connectors.  They are fully compatible with the original Deans connectors. Sold in packs of 5 pairs.
 
NOTE:  The polarity is marked on these connectors on the back of each half, a very tiny + and - sign that is molded into the nylon body of the connector itself. Even though they can be wired any way you like, I suggest you follow the polarity marked on them, as this will be compatable with lots of other commercially manufactured products, like Li-Po batteries and ESCs.