My favorite is TripAdviser and I find photos posted (not by management but by reviewers) helpful.
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I use this heavily as well, and I do annual travel to Europe. And these days they show hotel prices available through various booking sites if you supply your dates. Looks like TripAdvisor is getting into the booking business themselves. [I always check with the hotel directly - the prices posted are just a rough guide and usually far more options, and sometimes nice discounts are available]. BTW - you can switch currency too - I prefer to see hotels in local currency for Europe.
On our planned trip to Hawaii, I have found several websites that are specific to Hawaii - or even to specific islands. So depending on where you go, just do a bunch of web searches. You might find something specific to the area that provides a lot more insight.
I always start with Google Flights for the airfare. That does a good comparison across airlines. And then when you whittle down to the flights you want, you can book directly with the airline.
Google flights saved my butt recently, because I simply could not find the flights I wanted on the United.com website. I think they've made some user interface changes and the searches/search criteria are horrible. For example, I couldn't select "no more than 2 stops", and United was only giving me 3 stop options for the times I wanted!
But when I pressed the "book directly with United" button on the Google Flights page, my selected flights were selected at the United.com site and I was able to proceed. Whew!
Flyertalk sometimes turns up something very useful, but this tends to be more on the lines of using ATM cards in foreign destinations, using EMV chip cards in Europe, and buying phone SIMs in various countries.