One of my favorite inexpensive DIY resources for improving your American English accent. It covers all the important elements of improved pronunciation, from words stress, linking, reductions, etc to difficult vowel & consonant sounds You can get this new 2nd edition as a physical book or electronic version. It also includes audio. With this book, you get a lot for a small price.
Oxford Learner's Dictionary My favorite online dictionary. Click on the microphone to hear the American English pronunciation. Also see the pronunciation written in IPA. If you need help understanding the symbols, just click on the "pronunciation" explanation on the right side of the screen.