Having five dogs and being a natural problem solver, I am always on the lookout for good tools and information on dealing with problem behaviors.
Listed below are several tools I have personally used and recommend:
(1) Pet Corrector - I am listing this one first because it is my favorite. When one barking dog sets off my other four, this tool is great to put an immediate squash on all barking. You simply say "No!" or whatever you want your word to be then push the button and it produces a hissing sound which startles your dog into being quiet. From that point on, all you usually have to do is pick up the can and they all immediately get quiet. This works great on four of my five dogs. Note: Don't overuse for many different behavior problems. Dogs can become desensitized if you overuse it.
(2) Pet Convincer 2 - This was recommended by my trainer. It is a more professional version of the Pet Corrector above. It also emits a hissing sound to help "reset' your dog's brain when barking, being aggressive, jumping, etc. It is rechargeable with C02 cartridges which can be purchased separately.
(3) Doggie Don't Device - This was also recommended by a professional trainer. It is used to "interrupt" the dog's thought to bring their focus back to you. It emits a "zapping" sound which gets your dog's attention very quickly. This is a great tool to stop jumping, barking or leash reactivity. I stick this in my back pocket on every walk.
(4) Dog Dazer II Ultrasonic Dog Deterrent - For whatever reason, my dogs feel the need to scuffle whenever I remove the full garbage bag from the can to take out. This little device stops the fight instantly. You can't hear it because it is ultrasonic, but the dogs jump back like something hit them. The garbage can theatrics are almost a memory now.
(5) ScatMat - This is a mat that you can place on your couch or anywhere else you do not want your pet. I used mine on the bottom step because I did not want my dogs upstairs. If they put a paw on it, it emits a loud beep and believe me, they back off. One of the many purchase options is a thin, narrow mat you can use in a window sill or on a counter top.
(6) Sentry Calming Collar - I used this collar on three of my dogs. It worked great on two of them and I saw marginal results on the third. If your dog is high strung or fearful, it is worth giving this collar a try. It's a bonus that it makes your dog smell great too. Amazon's cost for a package of three is way below what you will pay in the pet store.
(7) Doberman Security Motion Alarm Detector with Infrared Sensor - This little alarm can be used in so many ways. You can use it to block off any area of your house you do not want your dog in. You can also use it to teach your dog to stay off the counter or furniture. It's also a great way to teach your dog to leave your food alone when you turn your back. I can't tell you how many times I have went to the bathroom to come back to an empty plate. Set them up a couple of times with this sensor and they won't go near it again. If your dog likes to sneak to a certain spot in your house to potty when you aren't looking, you can break that habit with this alarm.
(8) Home Security Camera with two-way audio - I have a camera on my dogs in the living room because that is where they spend 99% of their time when we aren't home. I can listen to them and talk to them through the camera. I have on several occasions logged in to find them howling. When five schnauzers howl, it's quite a little party. I spoke to them through the camera and told them to knock it off and they stopped. However, the camera I have cost eight times as much as this little guy. I'm liking what I see about this camera and may purchase one to expand my viewing area.
(9) Elevated Pet Bed - I now own five of these beds. If you do not teach any other obedience commands, you should definitely consider teaching "Place". It is the best dog obedience command out there. This hammock is great to designate your dog's "Place". We use the command "Place" several times a day now with our dogs: when someone rings the doorbell, when we have company, when I am fixing their meals, or when I just need them to be quiet, still and get out from under my feet. Here is a link to a great YouTube video about how to teach "Place". 
(10) Thundershirt - I have used this on two of my dogs. Abby used it when she was in obedience training to help calm her around other dogs. I use it on Bella when we have thunderstorms because she is terrified of loud noises. It works great for both. If you have a dog who is anxious in the car, this would be great for that too.I hope you can find a solution for your dog(s)' behavior issues within this post. With five dogs, I am always running into something that needs attention and the above tools have helped out tremendously.
Here's a video of three of the girls going to their "Place":
