I've just completed a massive cross-country US road trip during which birding was almost always at the forefront of how I choose where to head next. Several tools helped me figure out where I could find either new birds to me or generally interesting birding.
First, a little more about me and my motivations when choosing birding locations. I consider myself a light lister. My life list is important to me, but I'm quite happy to have a good hike without focusing too much on the species count. I also carry a point and shoot for photographing birds. Finally, I usually travel with folks who aren't as heavily into birding as me, so these tips will be just as good for finding generally interesting hikes.
Absolutely nothing will beat a good guided tour. Getting an experienced birder to show you around is sure to make the best use of your time, especially if you aren't going to be in one spot for very long. Some Audubon chapter websites have listings of local tour guides. Pelagic boat tours, if you're near the ocean, can also be excellent.
These will usually require a bit of advance planning ahead to arrange and are much easier to do in birding-specific destinations like South Texas or Southeast Arizona. Keep an eye out and try to get one set up if you end up in a big birding spot!
The best resource available to you is a local birder. Above all else, this is the easiest way to find interesting places to check out birds and get tips about rarities. I had great luck at tourist information centers - they're almost always staffed by a nice retiree that either birds themselves or knows someone who does. Park rangers or other park staff are also great resources. Especially on a meandering road trip, getting to a local as early as possible is the best way to get the most out of your time in an area. Zoos and aquariums are also good places to ask questions.
In a similar vein, Audubon chapters are a good starting point for local bird info. Check for birding outings and join them if there is room. If there isn't, you'll at least have a list of good spots to check on your own.
When you're doing pre-trip research, the most powerful tool available is eBird's hotspot map. Explore the areas near where you'll be in advance of your arrival. Good indicators of a great birding trip are a high number of submitted checklists at a location - even more than the total number of species. High traffic hotspots are great because you'll not only encounter birds - you'll also find other birders. Do note that some high traffic locations are sensitive to the time of the year - like hawk watches in the fall. So, be sure to pair ebird hotspots with a cursory google about the location keeping the time of year in mind.
Another way to use eBird is to check the Target Species for a county or state you'll be visiting. If you are a lister or just get more excited about new birds, this is the best way that I found to get some quickly. Target Species can be found in the right sidebar when you go to a region in eBird - here is Travis County TX, for example. Switch the For your... section to World to get a list of lifers for you in that area. Also handy when you're back home if you want to boost your county count!
It is worth having a comprehensive guide on the birds of North America. You should skim the pages regularly and/or when you see a new bird always familiarize yourself with the other birds on the pages. A larger guide is especially relevant if you are travelling during migration, as you will have the chance of encountering many more birds than a local guide is likely to cover. Local guides are worth a look to check for local specialty birds, but will usually be missing a lot of what you will see.
As for specific recommendations, The Sibley Guide to Birds tends to be people's favorite from what I can tell. My first book was a Peterson Field Guide to Birds of North America and I still carry it with me. There is also Birds of North Amaerica by Kenn Kaufman as a third option. The best way to choose is to go to a library or book store and see which one you like the most, but if you aren't able to you can't go wrong with Sibley.