How to fine the best prices when shopping online?

Hi,

Every time I shop online I realize that I'm able to save and find better deals depending on the search engine I use.
These are the ones I use before I decide on the best deal (price, shipping cost & time, condition etc'):

https://www.google.com/shopping - shopping search from Google
http://www.shopzilla.com/ - same company as bizrate - almost as big as google (sometimes better prices)
http://www.pricegrabber.com/ - great for US stores
https://www.dealnews.com/ - great deals sometimes
https://bestsavings.online/ - good way to compare amazon & ebay results
https://slickdeals.net/ - daily deals & coupons

Please share your best shopping sites too...