Different consonant groups often prove to be the most difficult sounds for learners of English, especially if they differ greatly from the sounds of their native language.

• The How now brown cow? course book in PUHUMO has good, thorough exercises on consonant sounds. You can either go through all of them or choose the sounds that are difficult for you.

• Minimal pair exercises can also be useful if you're having trouble with specific sounds.
  

• Easton English Pronunciation: Here you can learn about all the consonant sounds of English and see the IPA symbols. Choose the sound and then listen to some examples.

• Peter Ladefoged's Vowels and Consonants: This page contains samples of all the consonant sounds, as well as many other topics ranging from the IPA chart sounds to talking computers.

• Virtual Language Centre: Here you can look at consonants either by the manner of articulation or place of articulation. You can also listen to samples and do exercises.