The Amazon Smart Plug typically retails for $24.99, but applying the promo code "AMZNPLUG" (without the quotes) will knock $20 off price, bringing it down to just $4.99. No hub is required for the Smart Plug, which means that you technically don't need an Echo device for it to function. You can simply set it up with the Amazon Alexa and app and immediately start running routines with it (i.e. setting a plugged-in lamp or fan to turn on/off at a certain time).
However, most will want to use it for the Alexa integration, which will allow you to control the outlet with just your voice. The Smart Plug provides control over just a single outlet, and its design is compact enough the at it won't block a second outlet on you wall plate. It supports 2.4GHz 802.11n, and will not work on 5GHz networks. In addition, the plug supports maximum output of 15A.
If you've used the AMZNPLUG code during previous Amazon promotions, this code won't work for you. So, this is only for first-time buyers, unfortunately. You can purchase the Amazon Smart Plug by clicking the following link.
A comparable alternative to the Amazon Smart Plug is the TP-Link HS05, which also doesn't require a hub, but will work with both Amazon Alexa andthe Google Assistant. It's priced at $17.99, and Amazon also a two-outlet TP-Link HS107 for $20.99.