I use the manufacturers websites to get HP ratings, weights, measurements, capacity, specs, to see what options are available, and to compare MSRP (new to new) from the different makers. You can also look at some different pics of the boats on the websites and see how they are laid out. This gives you an idea of what you want or can afford used.
You can then use the manufacturers websites to find a dealer in your area. Go look at the boats you like/are interested in at a dealership in person. Sometimes you think a boat is what you want when looking at pics on the computer then when you see it in person its really not that great. Or its alot smaller or bigger than you thought it was. Bass Pro is awesome for this because they usually have a lot of different boats in stock and you can walk around and compare the sizes (a 1654 is a 1652 no matter what the manufacturer) even if you are not interested in a tracker it will give you a good idea of what you want. If you ARE interested in a tracker they will finance you on the spot. Boat, Motor, Trailer, out the door!
This also gives you an opportunity to talk to a knowledgable person (hopefully) about the boat. Sometimes you can find some good deals on used trade in boats at dealer as well. You might just stumble upon the perfect boat while your there, or run into a guy who knows a guy who has a boat that might be for sale. LOl This happens all the time.
After you do all that, search Craigslist for the one you want at a discount.