These are some sites I like and how I use them:

SEARCHES:

Google Flights:  https://www.google.com/flights searches for flights.  I use Kayak more frequently, but it does the same thing.

Google Flights Explore:  https://www.google.com/flights/explore/ similar to Kayak Explore, but with bar charts.  

Kayak:  https://www.kayak.com/ searches airlines, hotels, car rentals for good deals.

Kayak Explore:  https://www.kayak.com/explore/ probably more fun than useful.  Put in an airport and it will tell you the best prices to go about anywhere.

Rome 2 Rio:  https://www.rome2rio.com/ this is a site I need to use more as a tool and not just for play.  It will let you daisy-chain many legs of a trip together and searches cars, trains, planes, sometimes boats.  

Skyscanner: https://www.skyscanner.com/ this is a great site for flexible air travel.

HOTELS/APARTMENTS

AirBnb:  https://www.airbnb.com/ affordable places to stay.  We use these all the time.  

Hotels.com:  https://www.hotels.com/ I use it begrudgingly.  Seems like the fine print is often a little too fine.

LaQuinta:  https://www.lq.com/en  affordable hotels in the US.  The points build up pretty fast.

EARN MONEY

Teach English as a Foreign Language:    http://www.teflonline.com/ offers on line certification for about $500.