Amazon offers the second-generation Amazon Echo Dot in Black or White for $39.99. (Several merchants are currently price-matching, including B&H Photo Video, Best Buy, and Bed Bath & Beyond.) Plus, Prime members receive free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.98.) That's the lowest total price we've seen and best deal we could find by $10. (For further comparison, last month we saw it available at this per-unit price, but you had to purchase two.) This voice-controlled device uses Alexa to play music (via Prime Music, Spotify, Pandora), control smart home devices (via Samsung SmartThings, Wemo, Nest), and do lots of other cool stuff (order a pizza via Domino's, order car service via Uber, play Jeopardy). It features 802.11n dual-band wireless, Bluetooth, and a 3.5mm audio output.

Update: Note that this item is temporarily out of stock at B&H Photo Video, but can still be ordered at this price for delivery when available.