There are so many online resources to actually book your flights and hotels that I don’t think it’s necessary to list them. But I will say that I always start with Google flights. It gives all the pertinent info. After I find a time and airline I like, I go to the specific carrier’s page or one of their alliance partners’ page to see if a reward seat is available.
I will mention 3 specific sites that might be useful in other ways. Skiplagged.com is a website that will search for flights that might be “hidden” from a normal search. Basically the premise is that it might be more expensive to find a flight between cities A and B vs. a flight between cities A and C with a layover in B. You would purchase the fare for the flights and then not get on the remaining leg of the flight. Of course, this only works if you don’t have any check bags.
Another site is expertflyer.com. Although there is a pay version of this site, there is a free version as well. The free version is more limited but gets the job done for the most basic of info. Primarily, if you’re looking to change seats to an aisle or maybe an exit row or maybe even an upgrade, this website can see which seats are available and alert you when that particular seat becomes available.
Finally, Seatguru.com provides the model aircraft for a certain route as well as the seating chart for that aircraft. It might be a small detail but if you’re a light sleeper, looking for extra legroom, or have any other personal quirks about where you sit, this is a pretty neat site to see which seat might suit you best.
These are just a few of my favorite sites to use when I’m planning my trip. There are many more out there but these are fun websites to play around to get info before you leave.