Where is the best place to get ws2812 strips
Best place? Probably Adafruit (well-tested, great support, fast shipping, etc). Cheapest place? Probably eBay or AliExpress.
I’ve bought all of mine on eBay, because I have more time (to wait for shipments) than money. Out of about 55 meters so far, only had one bad 5-meter reel. It was an easy to fix connection issue, but mentioned it to the seller and got some connectors and replacement WS2812B’s shipped to me free.
That’s not a recommendation for eBay – just my experience to date.
@allanGEE I have been looking for 3pin quick connect connectors for sometime now. Have found plenty of 4pin style
Like these? Search for 3 pin jst sm https://www.amazon.com/hkbayi-50Pair-50sets-Connector-WS2812B/dp/B00NBSH4CA
@Don_Hatcher Make sure you get the right width, but there are a ton of connectors on AliExpress. I just searched 3pin LED connector and found these as an example:
If you mean the ones like @Jason_Coon linked to, I got the same on eBay for $8 US… but I imagine Amazon will get them to you much faster for the extra $5.
I have no experience with the ones @Chris_Creel has linked to. I prefer to solder and reduce the chances of a broken connection later – a habit I picked to help avoid homemade quadcopters from falling out the sky at inopportune times. 
I have had a great experience buying from http://blueviewled.com quality products and excellent customer service. Slightly more expensive than the ebay/aamazo/alibaba route, but heaper than adafruit.